Crimped composite fiber, and fibrous mass and testile product using the same

ABSTRACT

A crimped conjugate fiber of the present invention is a conjugate fiber containing a first component and a second component, the first component containing polybutene-1 and linear low density polyethylene, the linear low density polyethylene content being 2 to 25 mass %, the second component 2 containing a polymer having a melting peak temperature at least 20° C. higher than the melting peak temperature of polybutene-1 or a polymer having a melting initiation temperature of 120° C. or higher, when viewed from a fiber cross-section, the first component occupies at least 20% of the surface of the conjugate fiber  10   and the centroid position of the second component not overlapping the centroid position of the conjugate fiber, the conjugate fiber is an actualized crimping conjugate fiber in which three-dimensional crimps have been developed or a latently crimpable conjugate fiber in which three-dimensional crimps are developed by heating. Accordingly, a crimped conjugate fiber having high elasticity, a high level of bulk recovery properties, and high durability against repetitive compression as well as high elasticity, a high level of bulk recovery properties, and high durability when used at high temperatures, and a fiber assembly that uses the crimped conjugate fiber are provided.

TECHNICAL FIELD

The present invention mainly relates to an actualized crimping conjugatefiber and a latently crimpable conjugate fiber suitable for a fiberassembly having high elasticity and a high level of bulk recoveryproperties, in particular a nonwoven fabric, and to a fiber assembly anda fiber product that use such a conjugate fiber.

BACKGROUND ART

Thermally bonded nonwoven fabrics containing a thermally fused conjugatefiber composed of a low-melting-point component that is exposed at leastpartially on the surface of the fiber and a high-melting-point componentthat has a melting point higher than that of the low-melting-pointcomponent are used in various applications, such as nonwoven fabricsused for hygienic materials, packaging materials, wet tissue, filters,wipers, and the like, nonwoven fabrics used for hard stuffing, chairs,and the like, and molded articles. In particular, as a urethane foamsubstitute, there is a growing demand for a nonwoven fabric havingexcellent elasticity and excellent bulk recovery properties, i.e.,having excellent thickness-direction bulk recovery properties, andextensive research has been made on a nonwoven fabric having excellentbulk recovery properties and a conjugate fiber suitable for such anonwoven fabric having excellent bulk recovery properties. Since aconjugate fiber suitable for a nonwoven fabric for use in suchapplications has itself excellent elasticity and shape recoveryproperties, research has been made on using the conjugate fiber itselfas wadding for various pieces of bedding such blankets and mattresses aswell as clothing articles.

Extensive research has been made on such a conjugate fiber that itselfhas excellent elasticity and a thermally bonded conjugate fiber that hasexcellent bulk recovery properties once it has been processed into afiber assembly such as a nonwoven fabric. Patent Documents 1 and 2 belowdisclose a conjugate fiber composed of a polyester component having amelting point of 200° C. or higher and a polyetherester block copolymercomponent, i.e., a so-called elastomer component, having a melting pointof 180° C. or lower. Use of the elastomer component as a sheathcomponent enhances the degree of freedom of bonded points and durabilityagainst compression deformation, and thus a fiber having a high level ofbulk recovery properties can be obtained.

Patent Document 3 discloses an actualized crimping conjugate fibercomposed of a first component containing a polytrimethyleneterephthalate (PTT)-based polymer and a second component that contains apolyolefin-based polymer, in particular, polyethylene, with crimpingbeing obtained by arranging the centroid position of the first componentso as not to overlap the centroid position of the fiber on thecross-section of the fiber. By including an actualized crimpingconjugate fiber in which a polymer having large bending elasticity andsmall bending hardness is used as a first component, in which thecross-section of the fiber is eccentric, and in which the crimps arewavy, a nonwoven fabric that has a high level of bulk recoveryproperties, that is flexible, and that has a large initial bulk can beobtained.

Patent Documents 4 and 5 disclose a crimped conjugate fiber containing asheath component containing polybutene-1 (hereinafter also referred toas PB-1) and a nonwoven fabric having excellent bulk recovery propertiesand improved initial bulk recovery properties that uses such a fiber.

In Patent Documents 1 and 2, a polyesterether elastomer is used as asheath component, and a nonwoven fabric having a high level of bulkrecovery properties is intended to be obtained by taking advantage ofthe fact that this polymer has rubberlike elasticity and a high degreeof freedom from bonding point deformation. However, since thispolyesterether elastomer is a copolymer of a hard polyester and a softether, and contains a soft component having low thermal resistance, thispolyesterether elastomer is readily thermally softened, and the nonwovenfabric undergoes bulk reduction, or so-called sagging, during thermalprocessing. As a result, a conjugate fiber in which such apolyesterether elastomer is used as a sheath component is problematic inthat the initial bulk when formed into a nonwoven fabric is small, onlygiving a highly dense nonwoven fabric, and its applications are thuslimited. Furthermore, such a nonwoven fabric being compressed whilebeing heated, or such a nonwoven fabric being repeatedly compressed isproblematic in that, for example, the points where pieces of the fiberare bonded to each other and the fiber itself collapse or bend, and thefiber strength is impaired, and thus the hardness of the nonwoven fabricis significantly lower than that of the original nonwoven fabric.

In Patent Document 3, it is intended to obtain a nonwoven fabric havinga high level of bulk recovery properties by selecting a specific polymerused for the core, a specific fiber cross-section, and a specific crimpstate. However, while the initial thickness (initial bulk) of thenonwoven fabric is large, the bulk recovery properties, in particularthe initial bulk recovery properties immediately after load removal, arenot sufficient, and thus there is a problem in that its applications arelimited.

The conjugate fiber disclosed in Patent Documents 4 and 5 is problematicin that, when a fiber web that uses the conjugate fiber is processedinto a nonwoven fabric in which pieces of the component fiber are bondedto each other by thermal processing, or when pieces of the resultingnonwoven fabric are bonded to each other by thermal processing, sincethe so-called sheath component that occupies for most of the fibersurface is composed of polybutene-1 and polypropylene, which has ahigher melting point than polybutene-1, a phenomenon occurs in which theapparent melting point of the sheath component is increased, and thermalbonding properties in a heat treatment at a low temperature and thestrength of the nonwoven fabric after thermal bonding are notsufficient, and it is also difficult to adjust the temperatureconditions for thermal bonding processing.

In addition to Patent Documents 1 to 5, extensive research has been madeon a nonwoven fabric having excellent bulk recovery properties, aconjugate fiber suitable for such a nonwoven fabric having excellentbulk recovery properties, a nonwoven fabric that uses such a fiber, andthe like, but there is still a problem in that deterioration of bulkrecovery properties is observed when a load is applied repetitively, anda fiber and a nonwoven fabric that are suitable for use in applicationssuch as cushioning materials for which a high level of bulk recoveryproperties are needed even after being repetitively compressed are notobtained.

CITATION LIST Patent Documents

Patent Document 1: JP H4-240219A

Patent document 2: JP H5-247724A

Patent document 3: JP 2003-3334A

Patent document 4: JP 2007-126806A

Patent document 5: JP 2008-248421A

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In order to solve the above-described problems of the conventional art,the present invention provides a crimped conjugate fiber having highelasticity, a high level of bulk recovery properties, and highdurability against repetitive compression as well as having highelasticity, a high level of bulk recovery properties, and highdurability when used at high temperatures, and a fiber assembly and afiber product that use such a fiber.

Means for Solving the Problem

The crimped conjugate fiber of the present invention is a conjugatefiber containing a first component and a second component, the firstcomponent containing polybutene-1 and linear low density polyethylene,the content of the linear low density polyethylene in the firstcomponent is 2 to 25 mass %, the second component containing a polymerhaving a melting peak temperature at least 20° C. higher than a meltingpeak temperature of polybutene-1 or a polymer having a meltinginitiation temperature of 120° C. or higher, when viewed from a fibercross-section the first component occupies at least 20% of the surfaceof the conjugate fiber and the centroid position of the second componentnot overlapping the centroid position of the conjugate fiber, and theconjugate fiber is an actualized crimping conjugate fiber in whichthree-dimensional crimps have been developed or a latently crimpableconjugate fiber in which three-dimensional crimps are developed byheating. The melting initiation temperature as used herein refers to anextrapolated melting initiation temperature measured by differentialscanning calorimetry (DSC) as defined in JIS-K-7121. Also, the meltingpeak temperature as used herein refers to a melting peak temperatureobtained from a DSC curve measured according to JIS-K-7121.

The fiber assembly of the present invention contains a crimped conjugatefiber in a proportion of 30 mass % or greater, and the crimped conjugatefiber is a conjugate fiber containing a first component and a secondcomponent, the first component containing polybutene-1 and linear lowdensity polyethylene. The content of the linear low density polyethylenein the first component is 2 to 25 mass %. The second component containsa polymer having a melting peak temperature at least 20° C. higher thanthe melting peak temperature of polybutene-1 or a polymer having amelting initiation temperature of 120° C. or higher. When viewed from afiber cross-section the first component occupies at least 20% of thesurface of the conjugate fiber and the centroid position of the secondcomponent not overlapping the centroid position of the conjugate fiber,and the conjugate fiber is an actualized crimping conjugate fiber inwhich three-dimensional crimps have been developed or a latentlycrimpable conjugate fiber in which three-dimensional crimps aredeveloped by heating.

The fiber product of the present invention at least partially containsthe fiber assembly of the present invention and is formed into hardstuffing, bedding, a vehicle seat, a chair, a shoulder pad, a brassierepad, a garment, a hygienic material, a packaging material, a wet wipe, afilter, a sponge-like porous wiping material, a sheet-like wipingmaterial, or wadding.

Effects of the Invention

In the crimped conjugate fiber of the present invention, the firstcomponent contains polybutene-1 and linear low density polyethylene, andthe second component contains a polymer having a melting peaktemperature at least 20° C. higher than the melting peak temperature ofthe polybutene-1 or a polymer having a melting initiation temperature of120° C. or higher, and accordingly the fiber exhibits excellentspinnability, stretchability, crimp formability, and like properties.Accordingly, use of the crimped conjugate fiber of the present inventionenables a conjugate fiber that has excellent bulk recovery propertiesand excellent thermal processability with which pieces of the fiber canbe strongly thermally bonded to each other even in low-temperaturethermal bonding processing as well as a fiber assembly and a fiberproduct that use the conjugate fiber to be obtained.

A nonwoven fabric that uses the crimped conjugate fiber of the presentinvention has both excellent initial bulk and excellent bulk recoveryproperties, and can be suitably used for cushioning materials and likehard stuffing, hygienic materials, packaging materials, filters,materials for cosmetics, women's brassiere pads, shoulder pads, and likelow-density nonwoven fabric products. Also, the crimped conjugate fiberof the present invention can be suitably used for wadding for variouspieces of bedding such as mattresses and blankets and various clothesdue to the sufficient elasticity and repulsive force of the fiberitself.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 shows the cross-section of a crimped conjugate fiberaccording to one embodiment of the present invention.

[FIG. 2] FIGS. 2A to 2C show forms of crimps of a crimped conjugatefiber according to one embodiment of the present invention.

[FIG. 3] FIG. 3 shows a form of conventional mechanical crimps.

[FIG. 4] FIG. 4 shows a form of crimps of the crimped conjugate fiber ofthe present invention in which wavy crimps and serrated crimps areconcomitantly present.

DESCRIPTION OF THE INVENTION

The crimped conjugate fiber of the present invention has highelasticity, a high level of bulk recovery properties, and highdurability against repetitive compression as well as having highelasticity, a high level of bulk recovery properties, and highdurability when used at high temperatures. In particular, a fiberassembly that uses the crimped conjugate fiber of the present inventionthat has actual crimps (hereinafter also referred to as an actualizedcrimping conjugate fiber) has large initial bulk. A fiber assembly thatuses the crimped conjugate fiber of the present invention that haslatent crimps (hereinafter also referred to as a latently crimpableconjugate fiber) develops crimps when multiple layers are placed oneover another and thermally processed. Accordingly, entanglement offibers between layers is enhanced, thus further increasing elasticityand bulk recovery properties.

First Component

In the crimped conjugate fiber of the present invention, the firstcomponent contains polybutene-1 and linear low density polyethylene.Disposing the first component such that the first component occupies forat least 20% of the surface of the conjugate fiber enables a crimpedconjugate fiber that makes use of the flexibility and the shaperetainability (resilience after being deformed) of polybutene-1 to beobtained.

It was found in the present invention that the first componentcontaining linear low density polyethylene in addition to polybutene-1improves spinnability such as uniform fiber formation and stretchabilityduring melt spinning as well as the spreadability of a staple fiber, thecrimp formability of a staple fiber, and like properties. That is, it isthought that, when melt spinning is performed solely with polybutene-1,the viscosity of the polymer discharged from a nozzle is not likely tobe stable, thus making it difficult to obtain a uniform fiber. Also,polybutene-1 has a high molecular weight, and the degree of freedom ofits molecular chain is poor and it is thus difficult to perform astretching step. In addition, polybutene-1 has very large heatshrinkability. Therefore, it is thought that the fiber would shrinkduring thermal processing, thus making it difficult to obtain a nonwovenfabric having good texture. However, since the first component containslinear low density polyethylene in addition to polybutene-1, theaforementioned problems such as poor spinnability and poorstretchability of polybutene-1 can be solved. Polybutene-1 has a largemolecular weight. That is, the molecular chain constituting polybutene-1is long, and entanglement between molecules is extensive, and it isthought that the aforementioned problem, i.e., poor stretchability, isthus created. Here, it is presumed that when the polymer componentcontains linear low density polyethylene in addition to polybutene-1 asin the present invention, linear low density polyethylene enters betweenthe molecular chains of polybutene-1 having high molecular weight, andadequately suppresses the entanglement of the molecular chains ofpolybutene-1, thus improving stretchability. In addition, due to the useof the polymer that contains linear low density polyethylene as thefirst component that occupies for most of the surface portion of thecrimped conjugate fiber, a fiber assembly that uses the resultingcrimped conjugate fiber exhibits excellent thermal processability(thermal treatment accomplished in a short period of time, uniformthermal bonding between component fibers) due to the linear low densitypolyethylene contained in the first component of the crimped conjugatefiber. That is, by adopting a configuration in which the principalcomponent of the first component that occupies for most of the surfaceof the crimped conjugate fiber is polybutene-1, and linear low densitypolyethylene is added in a proportion of 2 to 25 mass % relative to thefirst component, the phenomenon of an increase of the apparent meltingpeak temperature of the first component resulting from addition of ahigh melting point polymer, which can occur when a polymer (for example,polypropylene) having a higher melting point than polybutene-1 is addedto polybutene-1, does not occur. Accordingly, the crimped conjugatefiber of the present invention can be thermally bonded so as to attainsufficient bonding strength even when thermal processing is performed ata lower temperature for a shorter period of time, and thus thepost-processability of a fiber assembly containing the crimped conjugatefiber is enhanced. Moreover, since linear low density polyethylene hasexcellent impact resistance, the fiber assembly of the present inventionin which pieces of the component fiber are thermally bonded by the firstcomponent containing linear low density polyethylene of the crimpedconjugate fiber of the present invention is unlikely to result inseparation and delamination of bonded points of the fiber even when usedin applications where a load is repetitively applied, and thus hasexcellent resistance to residual set from repetitive compression as wellas resistance to residual set from compression.

The linear low density polyethylene is not particularly limited, and forexample, copolymers with α-olefins polymerized using Ziegler catalystsand metallocene catalysts are usable. From the viewpoint of attaining anarrow molecular weight range and a uniform branch distribution, it ispreferable to use copolymers with α-olefins polymerized usingmetallocene catalysts. A feature of linear low density polyethylenepolymerized using a metallocene catalyst is having a uniformdistribution of molecular weight, composition, and crystallinity. Due tothe foregoing feature, linear low density polyethylene polymerized usinga metallocene catalyst is likely to be uniformly dispersed inside PB-1even when added in an amount of 2 to 25 mass %, and it is thus presumedthat linear low density polyethylene demonstrates an effect of improvingthe stretchability of PB-1. The α-olefins are not particularly limited,and examples include 1-butene, 1-hexene, 1-octene, 1-pentene,3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene,1-decene, 1-dodecene, 1-tetradecene, 1-octadecene, and the like. As thecopolymer polymerized with an α-olefin using a metallocene catalyst,commercially available products such as “Harmorex” (registeredtrademark) NJ744N, “Kernel” (registered trademark) KS560T and KC571manufactured by Japan Polyethylene Corporation, and 420SD manufacturedby Ube-Maruzen Polyethylene Co., Ltd., may be used.

It is preferable that the linear low density polyethylene in the firstcomponent has a ratio (Q value) of weight average molecular weight (Mw)to number average molecular weight (Mn) of 6 or less. A more preferableQ value is 2 to 5, and a particularly preferable Q value is 2.2 to 3.5.The stretchability of the crimped conjugate fiber of the presentinvention containing polybutene-1 in the first component is enhancedwhen the first component contains, in addition to polybutene-1, linearlow density polyethylene, preferably linear low density polyethylenethat is polymerized using a metallocene catalyst and that satisfies theforegoing Q value range. In addition, the first component that occupiesfor most of the fiber surface, which contains linear low densitypolyethylene, imparts a slide effect to the fiber surface, and theresulting crimped conjugate fiber exhibits enhanced crimper passabilityand, once cut so as to obtain a staple fiber having a desired fiberlength, enhanced spreadability of the staple fiber, and thus such afirst component is preferable.

From the viewpoint of attaining good compatibility with PB-1, it ispreferable that the density measured according to JIS-K-7112 of thelinear low density polyethylene is 0.930 g/cm³ or less, more preferably0.920 g/cm³ or less, and particularly preferably 0.915 g/cm³ or less.When the density is within the foregoing range, compatibility with PB-1is good and heat resistance is high. The lower limit of the density ofthe linear low density polyethylene is not particularly limited, and itis preferably 0.870 g/cm³ or greater, more preferably 0.880 g/cm³ orgreater, and particularly preferably 0.890 g/cm³ or greater. When thedensity of the linear low density polyethylene is less than 0.870 g/cm³,the heat resistance of the first component constituting the crimpedconjugate fiber is likely to be impaired, and it is likely that bulkrecovery properties and resistance to residual compression set attemperatures greater than room temperature, for example in the range of40 to 80° C., are impaired.

From the view point of attaining good compatibility with PB-1 and goodelasticity of the resulting fiber as well as good bulk recoveryproperties and resistance to residual compression set of a fiberassembly prepared using the resulting crimped conjugate fiber, it ispreferable that the flexural modulus measured according to JIS-K-7171 ofthe linear low density polyethylene is 800 MPa or less, more preferably20 to 650 MPa, particularly preferably 25 to 300 MPa, and mostpreferably 30 to 180 MPa. When the flexural modulus is within theforegoing range, compatibility with PB-1 is good and heat resistance ishigh, and the resulting fiber assembly exhibits excellent bulk recoveryproperties and resistance to residual compression set. When the flexuralmodulus of the linear low density polyethylene is high, the flexibilityof the polymer is lost, and the elasticity of the resulting crimpedconjugate fiber tends to be impaired, and when the flexural modulus ofthe linear low density polyethylene exceeds 800 MPa, the bulk recoveryproperties and the resistance to residual compression set of a fiberassembly prepared using the resulting crimped conjugate fiber are likelyto be impaired. Also, when the flexural modulus of the linear lowdensity polyethylene is high, the melting peak temperature of thepolymer tends to be low, and when the flexural modulus of the linear lowdensity polyethylene is less than 20 MPa, heat resistance is impaired,and the bulk recovery properties of the resulting fiber assembly at hightemperatures are likely to be impaired.

It is preferable that the linear low density polyethylene has a meltingpeak temperature obtained from a DSC curve measured according toJIS-K-7121 of 70 to 130° C., more preferably 80 to 125° C., and evenmore preferably 90° C. to 123° C. When the melting peak temperature is70 to 130° C., heat resistance is high, and bulk recovery properties athigh temperatures are good. The term “melting peak temperature” as usedherein refers to a melting peak temperature obtained from a DSC curvemeasured according to JIS-K-7121. Herein, the melting peak temperatureobtained from a DSC curve is also referred to as a melting point.

It is preferable that the linear low density polyethylene has a meltflow rate

(MFR; a measurement temperature of 190° C., a load of 2.16 kgf (21.18N), hereinafter referred to as MFR190) according to JIS-K-7210 of 1 to30 g/10 min, more preferably an MFR190 of 3 to 25 g/10 min, and evenmore preferably 5 to 20 g/10 min. When the MFR190 is 1 to 30 g/10 min,heat resistance is good and bulk recovery properties at hightemperatures are favorable, and spun yam retrievability andstretchability are good.

It is preferable that polybutene-1 for use in the present invention hasa melting peak temperature obtained from a DSC curve measured accordingto JIS-K-7121 of 115 to 130° C., and more preferably 120 to 130° C. Whenthe melting peak temperature is 115 to 130° C., heat resistance is high,and bulk recovery properties at high temperatures are good.

It is preferable that the polybutene-1 has a melt flow rate (MFR; ameasurement temperature of 190° C., a load of 2.16 kgf (21.18 N),hereinafter referred to as MFR190) according to JIS-K-7210 of 1 to 30g/10 min, more preferably an MFR190 of 3 to 25 g/10 min, and even morepreferably 3 to 20 g/10 min. When the MFR190 is 1 to 30 g/10 min,polybutene-1 has a high molecular weight, and thus heat resistance isgood and bulk recovery properties at high temperatures are favorable,and thus this configuration is preferable. Also, spun yarnretrievability and stretchability are good.

In the first component, polybutene-1 is the principal component and iscontained in a proportion of 70 mass % or greater relative to the entirefirst component. From the viewpoint of attaining good productivity, goodcushioning properties, and good bulk recovery properties at hightemperatures, it is preferable that polybutene-1 is contained in aproportion of 75 to 98 mass %, more preferably 80 to 97 mass %,particularly preferably 85 to 97 mass %, and most preferably 87 to 96mass %.

By blending linear low density polyethylene that demonstrates asufficient compatibilizing effect with polybutene-1 as described above,a problem that occurs because the spinnability and stretchability ofpolybutene-1 are not improved when the compatibilizing effect onpolybutene-1 is excessively low, i.e., a uniform conjugate fiber isunlikely to be obtained, can be solved.

The amount of the linear low density polyethylene added to the firstcomponent is 2 to 25 mass %, when the entire first component being 100mass %, more preferably 3 to 20 mass %, particularly preferably 3 to 15mass %, and most preferably 4 to 12 mass %. When the amount is withinthe foregoing range, the flowability of PB-1 is enhanced, stable anduniform spinning can be performed, and stretchability is also improved.

The first component contains polybutene-1 and linear low densitypolyethylene as described above, and further may contain anethylene-ethylenic unsaturated carboxylic acid copolymer. Since theethylene-ethylenic unsaturated carboxylic acid copolymer, as with thelinear low density polyethylene, shows, compatibility with polybutene-1,the first component further containing an ethylene-ethylenic unsaturatedcarboxylic acid copolymer is capable of improving spinnability such asuniform fiber formation when melt spinning, stretchability, and thelike. Moreover, with a crimped conjugate fiber in which the firstcomponent further contains an ethylene-ethylenic unsaturated carboxylicacid copolymer in addition to polybutene-1 and linear low densitypolyethylene, when performing thermal processing such as thermal bondingon a fiber web or a nonwoven fabric containing the fiber, a phenomenonin which the sheath component undergoes shrinking and thermally bondedpoints shrink, i.e., “bonding point shrinkage” (hereinafter also simplyreferred to as bonding point shrinkage) is unlikely to occur at thepoints where pieces of the constituting fiber are thermally bonded toeach other, even when the thermal processing is performed for a longperiod of time at high temperatures. Accordingly, pieces of theconstituting fiber can be bonded firmly to each other, and a thermallybonded nonwoven fabric having greater bonding strength can be obtained.

The ethylenic unsaturated carboxylic acid constituting theethylene-ethylenic unsaturated carboxylic acid copolymer for use in thecrimped conjugate fiber of the present invention is not particularlylimited, and examples include acrylic acid, methacrylic acid, ethacrylicacid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate,monoethyl maleate, maleic anhydride, itaconic anhydride, and the like.

Specific examples of the ethylene-ethylenic unsaturated carboxylic acidcopolymer include ethylene-acrylic acid copolymer (EAA),ethylene-methacrylic acid copolymer (EMAA), ethylene-ethacrylic acidcopolymer, ethylene-maleic acid copolymer, ethylene-fumaric acidcopolymer, ethylene-itaconic acid copolymer, ethylene-maleic anhydridecopolymer, ethylene-itaconic anhydride copolymer, and the like. Amongsuch examples, ethylene-acrylic acid copolymer, ethylene-methacrylicacid copolymer, and ethylene-maleic acid copolymer are preferable, andethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymerare more preferable.

The ethylene-ethylenic unsaturated carboxylic acid copolymer is notlimited to a copolymer composed of ethylene and an ethylenic unsaturatedcarboxylic acid, and may be a copolymer in which another component iscopolymerized, including, for example, a terpolymer in which two or morecomponents including an ethylenic unsaturated carboxylic acid arecopolymerized with ethylene.

Examples of monomers for use as the other copolymerization componentsinclude ethylenic unsaturated carboxylic acid esters such as vinylacetate, vinyl propionate, and like vinyl esters, methyl acrylate, ethylacrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate,isooctyl acrylate, and like acrylic acid esters, methyl methacrylate,isobutyl methacrylate, and like methacrylic acid esters, and dim ethylmaleate, diethyl maleate, and like maleic acid esters; carbon monoxide;sulfur dioxide; and the like.

The copolymer in which ethylene, an ethylenic unsaturated carboxylicacid, and an optional copolymerization component are copolymerized isnot particularly limited, and an example may be anethylene-acrylate-maleic acid polymer in which ethylene, maleicanhydride and an acrylic ester are copolymerized (“Bondine” (registeredtrademark) manufactured by Arkema Japan) or the like.

The content of the ethylenic unsaturated carboxylic acid inethylene-ethylenic unsaturated carboxylic acid copolymer is 1 to 50 mass%, and preferably 1 to 29 mass %. In particular, in the case of acrylicacid, it is preferably 5 to 25 mass %, and in the case of methacrylicacid, it is preferably 5 to 20 mass %. The content of the othercopolymerizable component in the ethylene-ethylenic unsaturatedcarboxylic acid copolymer is in the range of 0 to 30 mass %, andpreferably 0 to 20 mass %.

In the present invention, as the ethylene-ethylenic unsaturatedcarboxylic acid copolymer, an ionomer in which carboxyl groups arepartially or entirely in a metal salt form can be used other than theethylene-ethylenic unsaturated carboxylic acid copolymer itself.Examples of metal species constituting metal ionomers include lithium,sodium, potassium, and like monovalent metals, magnesium, calcium, zinc,copper, cobalt, manganese, lead, iron, and like polyvalent metals, andthe like, with monovalent metals or zinc being particularly preferable.

In the present invention, the ethylene-ethylenic unsaturated carboxylicacid copolymers may be used singly, or may be used in a combination oftwo or more.

The ethylene-ethylenic unsaturated carboxylic acid copolymers can beobtained by, although not particularly limited to, high pressure radicalcopolymerization. The ethylene-ethylenic unsaturated carboxylic acidcopolymer ionomers can be obtained by ionizing the ethylene-ethylenicunsaturated carboxylic acid copolymers by an ordinary method.

As described above, the first component of the crimped conjugate fiberof the present invention contains an ethylene-ethylenic unsaturatedcarboxylic acid copolymer that demonstrates a sufficient compatibilizingeffect on polybutene-1, and accordingly a problem that occurs due to thepoor spinnability of polybutene-1 when the compatibilizing effect onpolybutene-1 is excessively low, i.e., a uniform conjugate fiber isunlikely obtained, can be solved. Also, a problem that occurs when thecompatibilizing effect on polybutene-1 is excessive, i.e., a conjugatefiber composed of a first component mainly containing polybutene-1 canbe obtained but bonding point shrinkage occurs due to thermal processingwhen preparing a thermally bonded nonwoven fabric from the resultingconjugate fiber, can be solved. That is, by blending anethylene-ethylenic unsaturated carboxylic acid copolymer thatdemonstrates a sufficient compatibilizing effect on polybutene-1, it ispossible to obtain a uniform conjugate fiber containing them. Moreover,the thermal bonding properties of the resulting conjugate fiber isimproved, and thus it is possible to overcome bonding point shrinkage,which can occur when bonding is performed by thermal processing attemperatures higher than the melting point of polybutene-1.

In the case where an ethylene-ethylenic unsaturated carboxylic acidcopolymer is added to the first component, it is preferable that theamount of the copolymer added is 0.5 to 20 mass %, when the entire firstcomponent being 100 mass %, more preferably 1 to 15 mass %, even morepreferably 3 to 10 mass %, and particularly preferably 4 to 9 mass %.When the amount is 0.5 mass % or greater, a crimped conjugate fiberhaving excellent thermal bonding properties can be obtained, the bondingstrength between pieces of the fiber is not impaired at hightemperatures, for example, a temperature of 190° C. or higher, and theaforementioned bonding point shrinkage does not occur. Moreover, whenthe amount is 20 mass % or less, a fiber structure such as a nonwovenfabric that has good hardness retainability (bulk recovery properties)can be obtained.

It is preferable that the ethylene-ethylenic unsaturated carboxylic acidcopolymer has an MFR190 measured according to JIS-K-7210 of 3 to 60 g/10min. A more preferable MFR190 is 5 to 40 g/10 min, and even morepreferably 5 to 30 g/10 min. With the MFR190 being 60 g/10 min or less,the effect of suppressing bonding point shrinkage that can occur whenperforming thermal processing on a fiber web that contains the resultingcrimped conjugate fiber can be enhanced. Moreover, with the MFR190 being3 g/10 min or greater, it is easy to obtain a uniform crimped conjugatefiber that has excellent operability during a spinning step and astretching step.

It is preferable that the ethylene-ethylenic unsaturated carboxylic acidcopolymer has a melting peak temperature obtained from a DSC curvemeasured according to JIS-K-7121 of 60° C. or higher, more preferably70° C. or higher, and even more preferably 70 to 120° C. With themelting peak temperature being 60° C. or higher, the effect ofsuppressing bonding point shrinkage is strong, and deterioration ofcushioning properties such as deterioration of bulk recovery propertiesand an increase of a rate of compression set due to thermal processingare unlikely to occur. Moreover, with the melting peak temperature being70 to 120° C., the effect of suppressing bonding point shrinkage, theeffect of suppressing deterioration of cushioning properties, and likeeffects can be more readily demonstrated.

It is preferable that the ethylene-ethylenic unsaturated carboxylic acidcopolymer has a softening temperature (Vicat softening point) asmeasured according to JIS-K-7206 of 40° C. or higher, more preferably50° C. or higher, and particular preferably 50 to 100° C. With thesoftening temperature being 40° C. or higher, the effect of suppressingbonding point shrinkage is strong, and deterioration of cushioningproperties such as deterioration of bulk recovery properties and anincrease of a rate of compression set due to thermal processing areunlikely to occur. With the softening temperature being 50 to 100° C.,the effect of suppressing bonding point shrinkage, the effect ofsuppressing deterioration of cushioning properties, and like effects canbe more readily demonstrated.

Examples of polymers that further can be blended with the firstcomponent, as long as the effect of the present invention is notimpaired, include polyolefin-based polymers other than theaforementioned polyolefin-based polymers, copolymerizable polymers witholefins having a polar group such as a vinyl group, a carboxyl group, ormaleic anhydride; polyolefin-based, styrene-based, polyester-based, andlike various thermoplastic elastomers; and the like.

It is possible to add various known additives to the first component aslong as the effect of the present invention is not impaired, or fiberproductivity, nonwoven fabric productivity, thermal bonding properties,and texture are not affected. Depending on the application, the firstcomponent can be mixed with, for example, other polymers, knownnucleating agents such as organic or inorganic substances (for example,calcium carbonate, talc, and the like), antistatic agents, pigments,delusterants, thermal stabilizers, photostabilizers, flame retardants(halogen-based, phosphorus-based, nonhalogen-based, antimony trioxide,and like inorganic compound-based flame retardants, and the like),bactericidal agents, lubricants, plasticizers, softening agents, and thelike. Adding a nucleating agent as such an additive brings about thefollowing advantages: an effect of preventing fusion between pieces ofthe fiber when spinning can be further enhanced, and a nonwoven fabrichaving soft texture can be obtained. The amount of nucleating agentadded is not particularly limited, and it is preferable in light offiber productivity to add a nucleating agent in a proportion of 20 mass% or less relative to the total mass of the first component, and it ismore preferable to add in a proportion of 10 mass % or less.

The first component constituting the crimped conjugate fiber of thepresent invention has the above-described features. That is, the firstcomponent contains PB-1 as the principal component in a proportion of 70mass % or greater, preferably 75 mass % or greater, and contains linearlow density polyethylene in a proportion of 2 to 25 mass %. Accordingly,the melting point of the first component after spinning is low, and thusa phenomenon in which the apparent melting point of the first componentis increased, which can occur in the case where polypropylene in placeof linear low density polyethylene is added to PB-1, is unlikely tooccur. This can be verified by performing measurement with adifferential scanning calorimeter (DSC) using the obtained crimpedconjugate fiber and then obtaining the melting point of each componentafter spinning from a heat of fusion curve obtained from themeasurement. That is, regarding the crimped conjugate fiber of thepresent invention, the first component after spinning has a meltingpoint (Tf1) obtained from a DSC curve measured according to JIS-K-7121of 140° C. or lower, preferably 90 to 135° C., more preferably 100 to130° C., particularly preferably 115 to 130° C., and most preferably120° C. to 125° C. As long as the melting point (Tf1) of the firstcomponent after spinning is within this range, a thermally bonded fiberassembly having sufficient bonding strength can be obtained at a lowertemperature in a shorter period of time when producing a fiber assemblysuch as a nonwoven fabric by thermal bonding processing. The higher themelting point of the first component after spinning, the less likely theabove-described effect is obtained, and if multiple melting point peaksderived from the first component appear, e.g., if the first componenthas a so-called double peak, at a temperature lower than the meltingpoint (Tf2) of the second component after spinning, which occurs whenthe melting point (Tf1) of the first component after spinning exceeds140° C. or when a polyolefin-based polymer (for example, polypropylene)having a high melting peak temperature is added, low-temperature thermalbonding properties are likely to be insufficient and a fiber assemblyhaving sufficient bonding strength is unlikely to be obtained. The lowerlimit of the melting point (Tf1) of the first component after spinningis not particularly limited, but when the lower limit is lower than 90°C., heat resistance and bulk recovery properties at high temperaturesare likely to be impaired. As described above, in the crimped conjugatefiber of the present invention, it is not preferable, regarding themelting point of the first component of the conjugate fiber afterspinning, that the heat of fusion curve has a so-called double-peakshape having multiple peaks derived from the first component whenperforming thermal bonding processing. Therefore, linear low densitypolyethylene is preferable that has a melting point that mostly overlapsthe melting point of post-spinning PB-1, which is the principalcomponent of the first component, and that has a so-called single peakhaving only one peak derived from the first component on a heat offusion curve.

Second Component

The second component of the crimped conjugate fiber of the presentinvention is not particularly limited as long as it is a polymer havinga melting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1 or a polymer having a melting initiationtemperature of 120° C. or higher. Polymers having excellent bendingstrength and bending elasticity are preferable, and examples includepolyethylene terephthalate, polybutylene terephthalate, polytrimethyleneterephthalate, polyethylene naphtahalate, polylactic acid, and likepolyester-based polymers, Nylon 6, Nylon 66, Nylon 11, Nylon 12, andlike polyamides, polypropylene, polymethylpentene, and likepolyolefin-based polymers, polycarbonates, polystyrenes, and the like.When such polymers are used as the second component, polymers may beused singly or may be used as a combination of two or more. In thecrimped conjugate fiber of the present invention, a polyester-basedpolymer or a polyolefin-based polymer is preferable as a polymer for usein the second component. The use of a polyolefin-based polymer as thesecond component together with the use of a polyolefin-based polymer asthe first component as described above makes it easy to recycle thecrimped conjugate fiber of the present invention. The crimped conjugatefiber of the present invention that uses the polyester-based polymer asthe second component has a large melting point difference between thesecond component that constitutes near the center of the conjugate fiberand the first component that occupies for most of the fiber surface, andtherefore even when the conjugate fiber, a fiber web, and a nonwovenfabric are subjected to thermal bonding at a temperature at which thefirst component undergoes sufficient thermal bonding, the secondcomponent maintains its shape, and sagging caused by thermal processingis unlikely to occur, and it is easy to manage the processingtemperature in a thermal processing step, allowing a fiber assemblyhaving high bonding strength to readily be obtained.

First, regarding the crimped conjugate fiber of the present invention, aconjugate fiber now will be described that uses a polyester-basedpolymer as a polymer constituting the second component. In the casewhere a polyester-based polymer is used as the second component of thecrimped conjugate fiber of the present invention, the polymer is notparticularly limited insofar as it is a polyester-based polymer having amelting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1 or a polyester-based polymer having amelting initiation temperature of 120° C. or higher. Since polymershaving excellent bending strength and bending elasticity are preferable,polyethylene terephthalate (hereinafter also referred to as PET),polytrimethylene terephthalate (hereinafter also referred to as PTT),and polybutylene terephthalate (hereinafter also referred to as PBT) arepreferable, with polyethylene terephthalate or polytrimethyleneterephthalate being more preferable. A polymer that has physicalproperties suitable for the application of the fiber is selected, and inthe case where a polyester-based polymer is used as the second componentin the crimped conjugate fiber of the present invention, it is mostpreferable to use polyethylene terephthalate in light of theavailability, the high bulk recovery properties of the fiber, and likefeatures.

It is preferable that the polyester-based polymer has a limitingviscosity [η] of 0.4 to 1.2, and more preferably 0.5 to 1.1. When thelimiting viscosity is less than 0.4, the molecular weight of the polymeris excessively low, and therefore not only is spinnability inferior butalso fiber strength is poor, and such a fiber is not practical. When thelimiting viscosity exceeds 1.2, the molecular weight of the polymer isincreased, and the melt viscosity is excessive. Therefore, single-yambreakage and like phenomena occur, making it difficult to perform goodspinning, and thus such limiting viscosity is not preferable. A limitingviscosity [η] within the foregoing range enables a conjugate fiberhaving excellent productivity and excellent bulk recovery properties tobe obtained. The limiting viscosity [η] as referred to herein ismeasured with an Ostwald viscometer using an o-chlorophenol solution at35° C. and expressed as a value obtained according to Expression 1below:

$\begin{matrix}{\lbrack\eta\rbrack = {\lim\limits_{c->o}{\frac{1}{\left\{ {C \times \left( {{\eta \; r} - 1} \right)} \right\}}.}}} & {{Expression}\mspace{14mu} 1}\end{matrix}$

In Expression 1 above, Θ_(r) is a value obtained by dividing theviscosity at 35° C. of a diluted solution of a sample dissolved ino-chlorophenol having a purity of 98% or greater by the concentration ofthe entire solvent measured at the same temperature, and C is the weightvalue in grams of the solute in 100 ml of the aforementioned solution.

It is preferable that the polyester has a melting peak temperatureobtained from a DSC curve measured according to JIS-K-7121 of 180° C. to300° C., and more preferably 200° C. to 270° C. A melting peaktemperature of 180 to 300° C. enables the weatherability to be increasedand the flexural modulus of the resulting conjugate fiber to beincreased.

Next, regarding the crimped conjugate fiber of the present invention, aconjugate fiber will now be described that uses a polyolefin-basedpolymer as a polymer constituting the second component. In the casewhere a polyolefin-based polymer is used as the second component of thecrimped conjugate fiber of the present invention, the polymer is notparticularly limited insofar as it is a polyolefin-based polymer havinga melting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1 or a polyolefin-based polymer having amelting initiation temperature of 120° C. or higher. Since polymershaving excellent bending strength and bending elasticity are preferable,polypropylene (hereinafter also referred to as PP) is preferable. Suchpolypropylene is not particularly limited, and for example,homopolymers, random copolymers, block copolymers, or mixtures thereof,and insofar as properties required for nonwoven fabrics and cushioningmaterials, such as heat resistance and bulk recovery properties, are notimpaired, polypropylene in which synthetic rubber or a like elastomercomponent is dispersed or mixed therewith may be used. In light of heatshrinkability, it is preferable that it is a homopolymer(homopolypropylene) or a block copolymer. In particular,homopolypropylene is advantageous in terms of the bulk recovery propertyand thus is preferable. Examples of the random copolymers and the blockcopolymers include copolymers of propylene and at least one α-olefinselected from the group consisting of ethylene and α-olefins having 4 ormore carbon atoms. Such α-olefins having 4 or more carbon atoms are notparticularly limited, and examples include 1-butene, 1-pentene,3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene,1-decene, 1-dodecene, 1-tetradecene, 1-octadecene, and the like. Inparticular, from the viewpoint of attaining bulk recovery properties,one selected from the group consisting of propylene homopolymers,ethylene-propylene copolymers, and ethylene-butene-1-propyleneterpolymers is preferable, and in light of heat resistance of theresulting crimped conjugate fiber, recycling efficiency after use, andeconomical efficiency (production costs), in the case where apolyolefin-based polymer is used as the second component, thepolyolefin-based polymer is particularly preferably homopolypropylene.From the viewpoint of attaining bulk recovery properties, in the casewhere a mixture of a homopolymer, a random copolymer, and a blockcopolymer of polypropylene is used, the homopolypropylene content is 73to 100 mass %, more preferably 75 to 100 mass %, particularly preferably85 to 100 mass %, when the entire second component being 100 mass %.

When polypropylene is used as the second component, it is preferablethat the polypropylene has a melt flow rate (MFR; a measurementtemperature of 230° C., a load of 2.16 kgf (21.18 N), hereinafterreferred to as MFR230) according to JIS-K-7210 of 3 to 40 g/10 min, anda more preferable MFR230 is 5 to 35 g/10 min. When the MFR230 is 3 to 40g/10 min, heat resistance is good and bulk recovery properties at hightemperatures are favorable, and spun yarn retrievability andstretchability are good.

When polypropylene is used as the second component, it is preferablethat the polypropylene has a ratio (Q value) of weight average molecularweight (Mw) to number average molecular weight (Mn) of 2 or greater. Amore preferable Q value is 3 to 12. A more preferable value of the ratio(Q value) of the weight average molecular weight (Mw) to the numberaverage molecular weight (Mn) of polypropylene in the second componentcan be selected according to the kind of three-dimensional crimps whichare developed in the resulting crimped conjugate fiber. For example, inthe case where an actualized crimping conjugate fiber in which a crimpedconjugate fiber has actualized three-dimensional crimps is to beobtained, the Q value of polypropylene of the second component ispreferably 4 to 12, and more preferably 5 to 9. In the case where alatently crimpable conjugate fiber that develops three-dimensionalcrimps once heated is to be obtained, the Q value is preferably 3 to 5.

When a polyolefin-based polymer such as polypropylene is used as thesecond component, in addition to the polyolefin-based polymer having amelting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1, a thermoplastic elastomer may also becontained. That is, in a constituent fiber of a fiber assembly suitablefor applications where excellent bulk recovery properties and resistanceto repetitive compression set are required, such as cushioning materialsand clothing pads, and in a crimped conjugate fiber for use as waddingof various pieces of bedding such as blankets and mattresses andclothing articles in which elasticity, shape recovery properties, andlight-weight properties of the fiber itself are required, the secondcomponent that contributes to the hardness, the bulk recoveryproperties, and the resistance to set of a crimped conjugate fiberitself and those of a fiber assembly containing the crimped conjugatefiber, or in other words, a component that is disposed more toward thecenter in a core-in-sheath conjugate fiber (also referred to as a corecomponent in a core-in-sheath conjugate fiber, encompassing an eccentricconjugate fiber) preferably contains a thermoplastic elastomer. Knownthermoplastic elastomers can be used, and styrene-based elastomers,olefin-based elastomers, ester-based elastomers, amide-based elastomers,urethane-based elastomers, and vinyl chloride-based elastomers areusable. Among such elastomers, in the crimped conjugate fiber of thepresent invention, in the case where a polyolefin-based polymer is usedas the second component, in light of recycling efficiency after use, itis preferable to use a polypropylene homopolymer, a random copolymer, ablock copolymer, or a mixture thereof as the polyolefin-based polymerthat has a melting peak temperature at least 20° C. higher than themelting peak temperature of polybutene-1, and it is preferable to use anolefin-based thermoplastic elastomer as the thermoplastic elastomer.Olefin-based thermoplastic elastomers are thermoplastic elastomers thatuse a polyolefin resin such as polyethylene or polypropylene as a hardsegment, and an ethylene-propylene-based rubber such asethylene-propylene rubber (EPM), ethylene-butene rubber (EBM),ethylene-propylene-diene rubber (EPDM) as a soft segment. Usableexamples of commercially available olefin-based thermoplastic elastomersinclude “Milastomer” (registered trademark) and “Notio” (registeredtrademark) manufactured by Mitsui Chemicals, Inc., “Espolex” (registeredtrademark) manufactured by Sumitomo Chemical Co., Ltd., “Thermorun”(registered trademark) and “Zelas” (registered trademark) manufacturedby Mitsubishi Chemical Corporation, and the like. In the crimpedconjugate fiber of the present invention, it is presumed that, in thecase where the second component constituting the crimped conjugate fiberis a polyolefin-based polymer, adding a suitable amount of athermoplastic elastomer, such as an olefin-based thermoplasticelastomer, to the second component imparts bending elasticity that seemsto be derived from the thermoplastic elastomer to the second componentcontaining the polyolefin-based polymer, and recoverability from bendingand resistance to repetitive bending fatigue, which are likely to beinsufficient in a conjugate fiber in which the second component iscomposed solely of a polyolefin-based polymer, are enhanced, anddurability against repetitive compression required in cushioningmaterials or the like are enhanced. Moreover, when the thermoplasticelastomer to be added is an olefin-based thermoplastic elastomer, thefirst component and the second component are both composed ofpolyolefin-based polymers, thus making it easy to recycle the fiberassembly after use.

In the crimped conjugate fiber of the present invention, in the casewhere the second component is a polyolefin-based polymer, it ispreferable that the olefin-based thermoplastic elastomer added to thesecond component is an α-olefin-based thermoplastic elastomer containingan α-olefin-based rubber-like polymer as a soft segment. Moreover, it ispreferable that the olefin-based thermoplastic elastomer and theα-olefin-based thermoplastic elastomer are olefin-based thermoplasticelastomers polymerized using metallocene catalysts.

The α-olefin-based rubber-like polymer is not particularly limited, andfor example, it is preferable to use a copolymer of ethylene and anα-olefin having 3 to 20 carbon atoms. Examples of the α-olefin includepropylene, 1-butene, 1-pentene, 3,3-dimethyl-1-butene,4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-decene, 1-dodecene,1-tetradecene, 1-octadecene, and the like. The hard segment contained inthe olefin-based thermoplastic elastomer is not particularly limited,and for example, polyolefin-based polymers such as polypropylene andpolypropylene are usable. The polypropylene is not particularly limited,and for example, homopolymers, random copolymers, block copolymers, ormixtures thereof are usable. Examples of the random copolymers and theblock copolymers include copolymers of propylene and at least oneα-olefin selected from the group consisting of ethylene and α-olefinshaving 4 or more carbon atoms. Such α-olefins having 4 or more carbonatoms are not particularly limited, and examples include 1-butene,1-pentene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene,4,4-dimethyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene,1-octadecene, and the like.

When a polyolefin-based polymer such as polypropylene is used as thesecond component, the content of the olefin-based thermoplasticelastomer added to the second component is preferably 3 to 25 mass %,more preferably 3 to 20 mass %, and particularly preferably 5 to 15 mass%, when the entire second component being 100 mass %. In the secondcomponent, when the olefin-based thermoplastic elastomer content is 3mass % or greater, the second component as a whole exhibits elasticitydue to the addition of the elastomer component to the second component,and the resistance to residual repetitive compression set and theresistance to residual compression set of a fiber assembly that uses thecrimped conjugate fiber of the present invention can be increased. Inthe second component, when the olefin-based thermoplastic elastomercontent is 25 mass % or less, a crimped conjugate fiber from which afiber assembly that has excellent resistance to residual repetitivecompression set and resistance to residual compression set is obtainedis produced without adversely affecting the spinnability and thestretchability of the crimped conjugate fiber.

The density of the olefin-based thermoplastic elastomer is preferably0.8 to 1.0 g/cm³, and more preferably 0.85 to 0.88 g/cm³. When thedensity is within the foregoing range, excellent heat resistance isobtained, and regarding a fiber assembly that uses the crimped conjugatefiber, a lighter fiber assembly can be obtained if the volume is thesame, and is thus preferably used in applications where a light weightis required.

The Shore A hardness of the olefin-based thermoplastic elastomermeasured according to ASTM D 2240 using a type A durometer is preferably50 to 95, more preferably 60 to 90, and particularly preferably 65 to85. When the Shore A hardness of the olefin-based thermoplasticelastomer added to the second component satisfies the foregoing range,the heat resistance and the durability against repetitive bending of anonwoven fabric that uses the resulting crimped conjugate fiber iswell-balanced. When the Shore A hardness is less than 50, the addedolefin-based thermoplastic elastomer itself is excessively soft, and theresulting crimped conjugate fiber and a fiber assembly deform easily,and thus bending recovery properties and bulk recovery properties can bepoor. When the Shore A hardness exceeds 95, the added olefin-basedthermoplastic elastomer is excessively hard, bending elasticityattributable to the addition of the olefin-based thermoplastic elastomerto the second component is not demonstrated, and bending recoveryproperties and bulk recovery properties against repetitive compressiontend to be impaired.

The melting peak temperature of the olefin-based thermoplastic elastomerused in the present invention is not particularly limited, but in lightof the heat treatment performed when producing a fiber assembly from theresulting crimped conjugate fiber as well as the application of thefiber assembly and the heat resistance of the fiber assembly, themelting peak temperature of the olefin-based thermoplastic elastomer ispreferably 70° C. or higher and 170° C. or lower, more preferably 100°C. or higher and 160° C. or lower, and particularly preferably greaterthan or equal to the melting peak temperature of polybutene-1 containedin the first component and 160° C. or lower. When the melting peaktemperature of the olefin-based thermoplastic elastomer contained in thesecond component is 70° C. or higher and 170° C. or lower, heatresistance is high, and bulk is not likely to be reduced in a thermaltreatment performed when obtaining a fiber assembly from the resultingcrimped conjugate fiber, thus enabling a bulky fiber assembly to bereadily obtained. In actual use of the fiber assembly, since the bulkrecovery properties at high temperatures are good, the crimped conjugatefiber and the fiber assembly are particularly suitable for applicationswhere heat resistance is required.

The melt flow rate of the olefin-based thermoplastic elastomer is notparticularly limited, and it is preferable that a melt flow rate (MFR; ameasurement temperature of 230° C., a load of 2.16 kgf (21.18 N),hereinafter referred to as MFR230) measured according to JIS-K-7210 of 1to 30 g/10 min, and a more preferable MFR230 is 3 to 20 g/10 min, and aparticularly preferable MFR 230 is 5 to 15 g/10 min. With the MFR230 ofthe olefin-based thermoplastic elastomer being within the foregoingrange, spun yarn retrievability and stretchability are good. Also, inaddition to the MFR230, with the melting peak temperature satisfying theforegoing range, the olefin-based thermoplastic elastomer used have goodheat resistance, and therefore bulk is not likely to be reduced in athermal treatment performed when obtaining a fiber assembly from theresulting crimped conjugate fiber, thus enabling a bulky fiber assemblyto be readily obtained. In actual use of the fiber assembly, since thebulk recovery properties at high temperatures are good, the crimpedconjugate fiber and the fiber assembly are particularly suitable forapplications where heat resistance is required.

While there are a variety of olefin-based thermoplastic elastomers thatsatisfy the aforementioned density, Shore A hardness, melting peaktemperature, and melt flow rate, among such olefin-based thermoplasticelastomers, it is preferable to use an olefin-based thermoplasticelastomer that is polymerized using a metallocene catalyst. In anolefin-based thermoplastic elastomer that is polymerized without using ametallocene catalyst, crystalline structure and amorphous structureportions having a size of 300 nm to 1 μm are scattered throughout theelastomer. With an elastomer in which such hard segments and softsegments having the aforementioned size are scattered throughout thepolymer, the bending elasticity of the elastomer itself and the bendingelasticity and the bulk recovery properties of a fiber and a nonwovenfabric that contain the elastomer tend to be poor, and in addition, ittends to be difficult to perform melt spinning. In contrast, in anolefin-based thermoplastic elastomer polymerized using a metallocenecatalyst, crystalline structure and amorphous structure portions havinga size of 5 to 50 nm are scattered throughout in the elastomer. Byadding an elastomer having such a structure to the second component(core component) of a crimped conjugate fiber, it is likely that theresulting crimped conjugate fiber has ample heat resistance andexcellent bulk recovery properties and resistance to set afterrepetitive deformation. An example of the olefin-based thermoplasticelastomer polymerized using a metallocene catalyst may be “Notio”(registered trademark) manufactured by Mitsui Chemicals, Inc., or thelike, but the olefin-based thermoplastic elastomer is not limitedthereto.

In the case where a polyester-based polymer is used as the principalcomponent of the second component as well as in the case where apolyolefin-based polymer is used as the principal component of thesecond component, the second component can be further blended with apolymer insofar as the effect of the present invention is not impaired.In addition, known various additives can be added also to the secondcomponent insofar as the effect of the present invention is not impairedand insofar as fiber productivity, nonwoven fabric productivity, thermalbonding properties, and texture are not adversely affected. Knownnucleating agents, antistatic agents, pigments, delusterants, thermalstabilizers, photostabilizers, flame retardants, bactericidal agents,lubricants, plasticizers, softening agents, and the like can be mixed asadditives that can be added to the second component according to theapplications.

In the crimped conjugate fiber of the present invention, the centroidposition of the second component does not overlap the centroid positionof the conjugate fiber. FIG. 1 shows a schematic diagram of thecross-section of a crimped conjugate fiber according to one embodimentof the present invention. A first component 1 is disposed around asecond component 2, and the first component 1 occupies for at least 20%of the surface of a conjugate fiber 10. Accordingly, the surface of thefirst component 1 melts during thermal bonding. A centroid position 3 ofthe second component 2 does not overlap a centroid position 4 of theconjugate fiber 10. As seen in an enlarged image of the cross-section ofthe crimped conjugate fiber captured with an electron microscope or thelike, the shift ratio (hereinafter also referred to as eccentricity) isa value represented by Expression 2 below, where the centroid position 3of the second component 2 is C1, the centroid position 4 of theconjugate fiber 10 is Cf, and a radius 5 of the conjugate fiber 10 isrf:

Eccentricity (%)=[|Cf−c1|/rf]×100  Expression 2

The fiber cross-section in which the centroid position 3 of the secondcomponent 2 does not overlap the centroid position 4 of the conjugatefiber is preferably in an eccentric core-in-sheath type as shown in FIG.1 or a parallel type. In some cases, even when the cross-section is in amulti-core type, a fiber in which the centroid position of a multi-coreportion as a whole does not overlap the centroid position of the fiberis usable. In particular, it is preferable that the fiber has aneccentric core-in-sheath cross-section because the desired wavy crimpsand/or spiral. crimps are readily developed. The eccentricity of theeccentric core-in-sheath conjugate fiber is preferably 5 to 50%, andmore preferably 7 to 30%. The shape of the fiber cross-section of thesecond component 2 may be, other than being circular, oval, Y, X, #,polygonal, star, and various other shapes, and the shape of thecross-section of the conjugate fiber 10 may be, other than beingcircular, oval, Y, X, #, polygonal, star, and various other shapes, orhollow.

With the cross-section of the crimped conjugate fiber of the presentinvention as shows in FIG. 1, in the case of an eccentric core-in-sheathstructure where the first component is disposed as a sheath component ofthe conjugate fiber, the second component is disposed as a corecomponent, and the centroid position of the second component does notoverlap the centroid position of the conjugate fiber. It is preferablethat the second component and the first component (core/sheath) arecombined in a volume ratio of 8/2 to 2/8, more preferably 7/3 to 3/7,and even more preferably 6/4 to 4/6. The second component that serves asa core component contributes mainly to bulk recovery properties, and thefirst component that serves as a sheath component contributes mainly tothe strength of the nonwoven fabric and the hardness of the nonwovenfabric. A combination ratio of 8/2 to 2/8 enables the strength, thehardness, and the bulk recovery properties of the nonwoven fabric to besatisfied simultaneously. When the first component that serves as asheath component is excessive, the strength of the nonwoven fabric isincreased, but the resulting nonwoven fabric tends to be hard, and thebulk recovery properties tend to be poor. On the other hand, when thesecond component that serves as a core component is excessive, bondingpoints are excessively reduced, and the strength of the nonwoven fabrictends to be lowered, and the bulk recovery properties tend to be poor.

FIG. 2 shows forms of crimps of a crimped conjugate fiber according toone embodiment of the present invention. The phrase “conjugate fiber inwhich three-dimensional crimps have been developed” as used herein meansthat the crimp shape have been developed in the crimped conjugate fiberincludes wavy crimps and/or spiral crimps. The term “wavy crimps” asused herein refers to crimps having curved crests as shown in FIG. 2A.The term “spiral crimps” refers to crimps having spirally curved crestsas shown in FIG. 2B. Crimps in which wavy crimps and spiral crimps areconcomitantly present as shown in FIG. 2C are encompassed within thecrimp form of the three-dimensional crimps developed in the crimpedconjugate fiber of the present invention. In the case of ordinarymechanical crimps as shown in FIG. 3, the crests of crimps are sharplyangled, i.e., retaining serrated crimps, and it tends to be difficult toattain large initial bulk when processed into a nonwoven fabric.Moreover, planar elasticity against compression, i.e., a spring effect,is inferior, and in particular, sufficient initial bulk recoveryproperties are not likely to be obtained. Crimps in which acutely angledcrimps by mechanical crimping and wavy crimps are concomitantly presentas shown in FIG. 4 and, although not shown in the figures, crimps inwhich acutely angled crimps of mechanical crimping and spiral crimps areconcomitantly present are also encompassed within the crimp form of thethree-dimensional crimps which are developed in the crimped conjugatefiber of the present invention.

Regarding the crimped conjugate fiber of the present invention, crimpsin which wavy crimps and spiral crimps are concomitantly present asshown in FIG. 2C are particularly preferable because cardability,initial bulk, and bulk recovery properties can be satisfiedsimultaneously.

Hereinbelow, a method for producing the crimped conjugate fiber of thepresent invention will now be described.

First, a method for producing an actualized crimping conjugate fiber,which is one embodiment of the crimped conjugate fiber of the presentinvention, will now be described.

First, a first component containing polybutene-1 and linear low densitypolyethylene and a second component containing a polymer having amelting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1 or a polymer having a melting initiationtemperature of 120° C. or higher are provided. Next, the first componentand the second component are supplied to a compound nozzle, for example,an eccentric core-in-sheath compound nozzle, such that on the fibercross-section, the first component occupies for at least 20% of thesurface of a conjugate fiber, and the centroid position of the secondcomponent does not overlap the centroid position of the conjugate fiber,and the second component is subjected to melt spinning at a spinningtemperature of 220 to 350° C., and the first component at a spinningtemperature of 200 to 300° C. The spinning temperature of the secondcomponent is selected according to the polymer, and it is preferable toperform melt spinning at a spinning temperature of 220° C. to 330° C. inthe case where a polyolefin-based polymer such as polypropylene orpolymethylpentene is used, and at a spinning temperature of 240 to 350°C. in the case where a polyester-based polymer such as polyethyleneterephthalate, polytrimethylene terephthalate, or polybutyleneterephthalate is used.

The first component and the second component are supplied to aneccentric core-in-sheath compound nozzle at the aforementioned spinningtemperatures, and retrieved at a retrieving rate of 100 to 1500 m/min togive an unstretched spinning filament having a fineness of 2 to 120dtex. Next, a stretching treatment is carried out at a stretch ratio of1.8 or greater at a stretching temperature of 40° C. or higher and lowerthan the melting point of the first component. A more preferable lowerlimit of the stretching temperature is 50° C. or higher, and a morepreferable upper limit of the stretching temperature is a temperature10° C. lower than the melting point of the first component. When thestretching temperature is lower than 40° C., crystallization of thefirst component barely proceeds, and thus thermal shrinkage tends to beincreased and bulk recovery properties tend to be reduced. When thestretching temperature is greater than or equal to the melting point ofthe first component, pieces of the fiber tend to fuse to each other. Amore preferable lower limit of the stretch ratio is 2. A more preferableupper limit of the stretch ratio is 4. When the stretch ratio is 1.8 orgreater, the stretch ratio is not excessively small, making it easy toobtain a fiber in which the above-described wavy crimps and/or spiralcrimps are developed, and the initial bulk and the rigidity of the fiberitself are not small, and nonwoven fabric processability such ascardability and bulk recovery properties are not inferior. Thestretching method is not particularly limited, and known stretchingtreatments can be performed, such as wet stretching in which stretchingis performed while heating with high temperature fluid such as hotwater; dry stretching in which stretching is performed while heating inhigh temperature gas or with a high temperature metal roll; and watervapor stretching in which stretching is performed while heating a fiberby water vapor having a temperature of 100° C. or higher under ordinarypressure or increased pressure. Among such methods, wet stretching usinghot water is preferable because of its productivity and economicalefficiency and because it allows the entire unstretched fiber bundle tobe readily and uniformly heated. Before or after the above-describedstretching, an annealing treatment may be performed as necessary under adry heat, wet heat, or steaming atmosphere at 90 to 120° C.

In an actualized crimping conjugate fiber that is one embodiment of thecrimped conjugate fiber of the present invention, in the case where thepolymer having a melting peak temperature at least 20° C. higher thanthe melting peak temperature of polybutene-1 or the polymer having amelting initiation temperature of 120° C. or higher contained in thesecond component constituting the actualized crimping conjugate fiber isa polyolefin-based polymer such as homopolypropylene, anethylene-propylene copolymer, or an ethylene-butene-1-propyleneterpolymer, the stretching temperature is preferably 40° C. or higherand lower than or equal to the melting peak temperature of polybutene-1contained in the first component, more preferably 50° C. or higher and100° C. or lower, and particularly preferably 60° C. or higher and 90°C. or lower. In contrast, in an actualized crimping conjugate fiber thatis one embodiment of the crimped conjugate fiber of the presentinvention, in the case where the polymer having a melting peaktemperature at least 20° C. higher than the melting peak temperature ofpolybutene-1 or the polymer having a melting initiation temperature of120° C. or higher contained in the second component constituting theactualized crimping conjugate fiber is a polyester-based polymer such aspolyethylene terephthalate, polytrimethylene terephthalate, orpolybutylene terephthalate, the stretching temperature is preferably 60°C. or higher and lower than or equal to the melting peak temperature ofpolybutene-1 contained in the first component, more preferably 70° C. orhigher and 100° C. or lower, and particularly preferably 75° C. orhigher and 95° C. or lower.

Next, before or after adding a fiber treating agent as necessary 5 to 25crimps per 25 mm are formed using a known crimper such as a stuffer-boxcrimper. A more preferable number of crimps is 8 to 20 per 25 mm, and aparticularly preferable number of crimps is 10 to 18 per 25 mm. It ispreferable that the shape of crimps after a fiber has passed through acrimper is serrated crimps and/or wavy crimps. When the number of crimpsis less than 5 per 25 mm, cardability tends to be impaired, and theinitial bulk and the bulk recovery properties of the nonwoven fabrictend to be poor. On the other hand, when the number of crimps is greaterthan 25 per 25 mm, the number of crimps is excessive, and not only doescardability tend to be impaired and the texture of the nonwoven fabrictend to deteriorate, but also the initial bulk of the nonwoven fabrictend to be reduced.

Moreover, after crimps are formed by the aforementioned crimper, it ispreferable to perform an annealing treatment at a temperature at whichan unstretched fiber bundle does not undergo thermal bonding and atwhich three-dimensional crimps are developed. For a conjugate fiber thatis encompassed within the crimped conjugate fiber of the presentinvention and in which the first component is composed of a polymercontaining polybutene-1, it is preferable to perform an annealingtreatment in a dry heat, wet heat, or steaming atmosphere in apreferable temperature range of 90 to 120° C. Specifically, it ispreferable that, after a fiber treating agent is added, crimps areformed by a crimper, and then an annealing treatment and simultaneouslya drying treatment are performed in a dry heat atmosphere of 90 to 120°C. because the process can be simplified. When an annealing treatment isperformed at a temperature of 90° C. or higher, dry thermal shrinkage isnot large, specific actual crimps are readily obtained, the texture ofthe resulting nonwoven fabric is not roughened, and productivity can beincreased. In the annealing treatment, a more preferable range of thetreatment temperature is 90 to 115° C., and particularly preferably 95to 110° C.

An actualized crimping conjugate fiber obtained by the above-describedmethod mainly has at least one type of crimp selected from wavy crimpsand spiral crimps shown in FIG. 2. Preferably, the actualized crimpingconjugate fiber has at least one type of crimp selected from wavy crimpsonly, spiral crimps only, crimps where wavy crimps and spiral crimps areconcomitantly present, and crimps where wavy crimps and serrated crimpsare concomitantly present, and particularly preferably, the actualizedcrimping conjugate fiber has at least one type of crimp selected fromwavy crimps only, spiral. crimps only, and crimps where wavy crimps andspiral crimps are concomitantly present. The number of crimps of theactualized crimping conjugate fiber is preferably 5 per 25 mm orgreater, and 25 per 25 mm or less, because a bulky nonwoven fabric canbe obtained without reducing cardability. Then, the fiber is cut into adesired fiber length, giving an actualized crimping conjugate fiber. Amore preferable number of crimps is 8 to 20 per 25 mm, and a particularpreferable number of crimps is 10 to 18 per 25 mm.

With the actualized crimping conjugate fiber, crimps appear on aconjugate fiber, and at least one type of three-dimensional crimpsselected from wavy crimps and spiral crimps are developed and madevisible, and therefore the actualized crimping conjugate fiber hasactual crimps. In the state of the fiber, the crimps may be actualizedcrimps in which three-dimensional crimps fully have been developed, ormay be actualized crimps in which slightly more crimping that will bedeveloped (that will be developed when the fiber is heated) remains.However, if crimps are developed to such an extent that the number ofcrimps exceeds 25 per 25 mm when heat is applied to the fiber (forexample, when heat is applied for processing into a nonwoven fabric asdescribed later), cardability may deteriorate, and it is thus notpreferable.

Next, a method for producing a latently crimpable conjugate fiber, whichis another embodiment of the crimped conjugate fiber of the presentinvention, will now be described.

First, a first component containing polybutene-1 and linear low densitypolyethylene and a second component containing a polymer having amelting peak temperature at least 20° C. higher than the melting peaktemperature of polybutene-1 or a polymer having a melting initiationtemperature of 120° C. or higher are provided. Next, the first componentand the second component are supplied to a compound nozzle, for example,an eccentric core-in-sheath compound nozzle, such that in the fibercross-section, the first component occupies for at least 20% of thesurface of a conjugate fiber, and the centroid position of the secondcomponent does not overlap the centroid position of the conjugate fiber,and the second component is subjected to melt spinning at a spinningtemperature of 220 to 350° C., and the first component at a spinningtemperature of 200 to 300° C. The spinning temperature of the secondcomponent is selected according to the polymer, and it is preferable toperform melt spinning at a spinning temperature of 220° C. to 330° C. inthe case where a polyolefin-based polymer such as polypropylene orpolymethylpentene is used, and at a spinning temperature of 240 to 350°C. in the case were a polyester-based polymer such as polyethyleneterephtha late, polytrimethylene terephthalate, or polybutyleneterephthalate is used.

The first component and the second component are supplied to aneccentric core-in-sheath compound nozzle at the aforementioned spinningtemperatures, and retrieved at a retrieving rate of 100 to 1500 m/min togive an unstretched spinning filament having a fineness of 2 to 120dtex. Next, a stretching treatment is carried out at a stretch ratio of1.5 or greater at a stretching temperature of 40° C. or higher and lowerthan the melting point of the first component. A more preferable lowerlimit of the stretching temperature is 50° C. or higher. A morepreferable upper limit of the stretching temperature is a temperature10° C. lower than the melting point of the first component. When thestretching temperature is lower than 40° C., crystallization of thefirst component barely proceeds, and thus thermal shrinkage tends to beincreased and bulk recovery properties tend to be reduced. When thestretching temperature is greater than or equal to the melting point ofthe first component, fibers each other tend to fuse. A more preferablelower limit of the stretch ratio is 2. A more preferable upper limit ofthe stretch ratio is 4. When the stretch ratio is 1.5 or greater, thestretch ratio is not excessively small, crimps are likely to appear whena thermal treatment is performed, and the initial bulk and the rigidityof the fiber itself are not small, and nonwoven fabric processabilitysuch as cardability and bulk recovery properties are not inferior. Thestretching method is not particularly limited, and known stretchingtreatments can be performed, such as wet stretching in which stretchingis performed while heating with high temperature fluid such as hotwater; dry stretching in which stretching is performed while heating inhigh temperature gas or with a high temperature metal roll; and watervapor stretching in which stretching is performed while heating a fiberby water vapor having a temperature of 100° C. or higher under ordinarypressure or increased pressure. Among such methods, wet stretching usinghot water is preferable because of its productivity and economicalefficiency and because it allows the entire unstretched fiber bundle tobe readily and uniformly heated.

In a latently crimpable conjugate fiber that is one embodiment of thecrimped conjugate fiber of the present invention, in the case where thepolymer having a melting peak temperature at least 20° C. higher thanthe melting peak temperature of polybutene-1 or the polymer having amelting initiation temperature of 120° C. or higher contained in thesecond component constituting the latently crimpable conjugate fiber isa polyolefin-based polymer such as a propylene homopolymer, anethylene-propylene copolymer, or an ethylene-butene-1-propyleneterpolymer, the stretching temperature is preferably 40° C. or higherand lower than or equal to the melting peak temperature of polybutene-1contained in the first component, more preferably 50° C. or higher and100° C. or lower, and particularly preferably 60° C. or higher and 90°C. or lower. In contrast, in a latently crimpable conjugate fiber thatis one embodiment of the crimped conjugate fiber of the presentinvention, in the case where the polymer having a melting peaktemperature at least 20° C. higher than the melting peak temperature ofpolybutene-1 or the polymer having a melting initiation temperature of120° C. or higher contained in the second component constituting thelatently crimpable conjugate fiber is a polyester-based polymer such aspolyethylene terephthalate, polytrimethylene terephthalate, orpolybutylene terephthalate, the stretching temperature is preferably 60°C. or higher and lower than or equal to the melting peak temperature ofpolybutene-1 contained in the first component, more preferably 70° C. orhigher and 100° C. or lower, and particularly preferably 75° C. orhigher and 95° C. or lower.

Next, before or after adding a fiber treating agent as necessary 5 to 25crimps per 25 mm are formed using a known crimper such as a stuffer-boxcrimper. Amore preferable number of crimps is 8 to 20 per 25 mm, and aparticularly preferable number of crimps is 10 to 18 per 25 mm. When thenumber of crimps is less than 5 per 25 mm or the number of crimpsexceeds 25 per 25 mm, cardability is likely to be impaired.

Furthermore, after crimps are formed by the aforementioned crimper, itis preferable to perform an annealing treatment in a dry heat, wet heat,or steaming atmosphere at 50 to 100° C., preferably 60 to 90° C., morepreferably 60 to 80° C., and particularly preferably 60 to 75° C.Specifically, it is preferable that, after a fiber treating agent isadded, crimps are formed by a crimper, and then an annealing treatmentand simultaneously a drying treatment are performed in a dry heatatmosphere of 50 to 90° C. because the process can be simplified. Anannealing temperature of 50 to 90° C. allows desired heat shrinkage tobe obtained, and a latently crimpable conjugate fiber can be obtained inwhich crimps are developed during heating. Also, a fiber that has highcardability can be obtained.

The crimped conjugate fiber of the present invention, i.e., theactualized crimping conjugate fiber or the latently crimpable conjugatefiber of the present invention, is subjected to the aforementionedannealing treatment and dried, and then the filament is cut according tothe application. The cut fiber length is 1 to 120 mm, but is selectedaccording to the application. If a nonwoven fabric is produced by aknown nonwoven fabric production method such as air-through, needlepunching, or hydro-entanglement, after producing a fiber web with acarding machine, the filament is cut into fiber lengths of 20 to 100 mm,preferably 30 to 90 mm, and more preferably 40 to 80 mm. If a nonwovenfabric is produced by a fiber web production method by air spreading,i.e., a so-called air-laid method, the filament is cut into fiberlengths of 1 to 40 mm, preferably 1 to 30 mm, and more preferably 3 to25 mm. If a wet nonwoven fabric is produced by a paper making method,the filament is cut into fiber lengths of 1 to 20 mm, preferably 1 to 10mm, and more preferably 3 to 8 mm. It is also possible with the crimpedconjugate fiber of the present invention that, depending on theapplication, the filament after an annealing treatment is not cut andused as it is.

The fineness of the crimped conjugate fiber of the present invention,i.e., the actualized crimping conjugate fiber or the latently crimpableconjugate fiber of the present invention, is not particularly limited.The crimped conjugate fiber is processed so as to have a finenesssuitable for applications, for example, various nonwoven fabricapplications such as hard stuffing that serves as a material substitutedfor urethane foam, mattresses for bedding, vehicle seats and variouschairs, cushioning materials for clothing such as a shoulder pad and abrassiere pad, sanitary materials, packaging materials, wet wipes,filters, sponge-like porous wiping materials, sheet-like wipingmaterials; applications as wadding for various kinds of bedding such asblankets and mattresses and clothing articles that make use of theelasticity and the shape recovery properties of the conjugate fiberitself, and like applications, but a fineness of 1 to 60 dtex ispreferable because elasticity as well as bulk recovery properties andtexture when processed into a nonwoven fabric are excellent. Amorepreferable fineness range is 2 to 50 dtex, particularly preferably 4 to30 dtex, and most preferably 4 to 20 dtex.

The fiber assembly of the present invention contains at least 30 mass %of the crimped conjugate fiber. When the crimped conjugate fiber iscontained in a proportion of 30 mass % or greater, the elasticity, thebulk recovery properties, and like properties of the fiber assembly canbe maintained at a high level. Examples of the fiber assembly includeknitted fabrics, woven fabrics, nonwoven fabrics, fillings, pads, fiberwebs, and the like. It is preferable that the fiber assembly contains 30to 100 mass % of the crimped conjugate fiber and 0 to 70 mass % offibers other than the crimped conjugate fiber. Such fibers other thanthe crimped conjugate fiber contained in the fiber assembly are notparticularly limited insofar as the performance of the crimped conjugatefiber is not impaired, including, for example, at least one fiberselected from synthetic fibers, chemical fibers, natural fibers, andinorganic fibers.

The method for producing a fiber assembly containing the crimpedconjugate fiber of the present invention is not particularly limited.After forming a fiber web by a known method, the fiber web can beprocessed into a nonwoven fabric by a known nonwoven fabric productionmethod such as air-through, needle punching, or hydro-entanglement. Inaddition, it is also possible that the crimped conjugate fiber isprocessed into a fiber ball, and the fiber ball is blown into a framemold and subjected to a thermal treatment to give a fiber assemblyhaving a specific shape as disclosed in JP 2001-207360A andJP2002-242061A. A production method is preferable in which a fiber webis formed and then processed into a nonwoven fabric. Examples of formsof the fiber web constituting the nonwoven fabric of the presentinvention include a parallel web, a semi-random web, a random web, across-laid web, a criss-cross web, an air-laid web, and the like. Thefiber web demonstrates a greater effect when the first component isbonded due to a thermal treatment. If necessary, the fiber web may besubjected to needle punching or hydro-entanglement before thermalprocessing. The means of thermal processing is not particularly limitedinsofar as the function of the crimped conjugate fiber of the presentinvention is sufficiently demonstrated, and it is preferable to use aheating machine that does not impose much pressure such as windpressure, for example, a heating machine that lets hot air through, aheating machine that vertically blows hot air, an infra-red heatingmachine, and the like.

Fibers that can be blended with a fiber web that uses the crimpedconjugate fiber of the present invention (hereinafter also referred toas blend fibers) are not particularly limited insofar as the performanceof the crimped conjugate fiber of the present invention is not impaired.Examples include single fibers of polyesters such as polyethyleneterephthalate, polybutylene terephthalate, polytrimethyleneterephthalate, polyethylene naphthalate, polylactate, and polybutylenesuccinate; single fibers of polyethylenes such as low densitypolyethylene, high density polyethylene, and linear low densitypolyethylene; single fibers of isotactic, atactic, syndiotactic, andlike polypropylenes polymerized using ordinary Ziegler-Natta catalystsand metallocene catalysts; single fibers of polyolefins such as polymersin which monomers of such polyolefins are copolymerized, or polyolefinsfor which metallocene catalysts (also referred to as Kaminsky catalysts)are used when polymerizing such polyolefins; single fibers of polyamidessuch as Nylon 6, Nylon 66, Nylon 11, and Nylon 12; single fibers of(poly)acryls composed of acrylonitrile; and single fibers of engineeringplastics such as polycarbonate, polyacetal, polystyrene, and cyclicpolyolefin. Here, the term “single fiber” refers to a fiber composedsolely of one polymer component. As the blend fiber, a conjugate fibercontaining at least one or more polymer components can also be usedinsofar as the performance of the crimped conjugate fiber of the presentinvention is not impaired. Examples of such a conjugate fiber includeconjugate fibers in which different types of resins among polyesters,polyolefins, polyamides and engineering plastics, or resins composed ofdifferent polymer components of the same type (for example, polyethyleneterephthalate and polytrimethylene terephthalate) are mutually combined.In the conjugate fiber, the combined state is not particularly limited.In terms of the cross-sectional shape of the fiber, core-in-sheathconjugate fibers, eccentric core-in-sheath conjugate fibers, parallelconjugate fibers, sectional conjugate fibers in which resin componentshaving a shape of citrus fruit clusters are disposed alternately, andsea-island conjugate fibers may be used. In the crimped conjugate fiberof the present invention, in the case where the second component is apolyolefin-based polymer, most of the polymer components constitutingthe crimped conjugate fiber are polyolefin-based polymers, and thus useof a single fiber composed of a polyolefin-based polymer, or use of aconjugate fiber in which polyolefin-based polymers are mutuallycombined, as a blend fiber is preferable from the viewpoint of recyclingefficiency of the fiber assembly.

Since the crimped conjugate fiber of the present invention has excellentthermal bonding properties, the crimped conjugate fiber exhibits thermalbonding properties for not only synthetic fibers having thethermoplastic resins as the components, but also natural fibersincluding cellulose-based fibers, semi-synthetic fibers (also referredto as regenerated fibers) such as viscose rayon, Tencel (registeredtrademark), Iyocel (registered trademark), and cuprammonium rayon,inorganic fibers such as glass fibers, and carbon fibers. Examples ofthe natural fibers include vegetable-based natural fibers andanimal-based natural fibers. Examples of vegetable-based natural fibersinclude fibers of ramie (China grass), linen (flax), kenaf, abaca(Manila hemp), henequen (sisal hemp), jute, hemp (cannabis), coconut,palm, paper mulberry, paper bush, bagasse, and the like. Examples ofanimal-based natural fibers include fibers of silk, sheep wool, angora,cashmere, mohair, and the like. As a fiber to be blended with thecrimped conjugate fiber of the present invention, a vegetable-basednatural fiber and an animal-based natural fiber can both be used, but avegetable-based natural fiber is preferable since the cost ofcultivation is inexpensive.

A fiber web containing the crimped conjugate fiber of the presentinvention can be processed into a bulky fiber assembly by performingthermal processing on the fiber web in a monolayer state, but a fiberassembly having superior bulkiness can be readily obtained by forming alaminate web in which fiber webs are stacked before performing thermalprocessing, or a laminate of fiber assemblies by stacking fiberassemblies after thermal processing. It is preferable that in the fiberassembly, fibers constituting the fiber assembly are arranged parallellyin the thickness direction of the fiber assembly, or in other words,fibers are arranged in the longitudinal direction of the fiber assembly.This is because fibers constituting the fiber assembly arrangedparallelly in the thickness direction afford good bulk recoveryproperties and cushioning properties against pressure applied in thethickness direction. Herein, the phrase “fibers constituting the fiberassembly are arranged parallelly in the thickness direction of the fiberassembly (arranged in the longitudinal direction of the fiber assembly)”means that the sharp angle formed by the fibers constituting the fiberassembly and the thickness direction of the fiber assembly is 45° orless, or in other words, when the fiber assembly is cut in the thicknessdirection and the cut surface is viewed with an optical microscope or ascanning electron microscope for enlargement, the sharp angle formed bythe fibers constituting the fiber assembly and the thickness directionof the fiber assembly is 45° or less. It is more preferable that 80% orgreater of the total number of the entire fibers constituting the fiberassembly viewed on a specific area of the cut surface are arranged inthe longitudinal direction of the fiber assembly. The fiber assemblydescribed above in which fibers constituting the fiber assembly arearranged parallelly in the thickness direction can be produced by aknown production method, and examples include so-called Strute nonwovenfabrics produced by shaping a fiber web into a wave form and subjectingit to thermal bonding while compressing it in the length direction, butthe fiber assembly is not limited thereto.

In the case where the crimped conjugate fiber contained in a fiber webis the actualized crimping conjugate fiber, the temperature of thermalprocessing on the fiber web is set so as to be within a range in whichthe developed wavy crimps and/or spiral crimps of the crimped conjugatefiber do not disappear during thermal processing. For example, if themelting peak temperature of polybutene-1 is Tm, the thermal processingtemperature is Tm−10 (° C.) to lower than the melting peak temperatureof the second component, preferably Tm−10 (° C.) to Tm+80 (° C.),particularly preferably Tm (° C.) to Tm+50 (° C.), and most preferably130 to 160° C. Due to the thermal processing, at least one resincomponent contained in the first component of the actualized crimpingconjugate fiber melts, and pieces of the constituent fiber are thermallyfused to each other. In particular, it is preferable that when pieces ofthe constituent fiber are thermally fused to each other by allowing atleast polybutene-1 of the actualized crimping conjugate fiber to melt,more rigid intersections where pieces of the fiber meet each other canbe formed, and bulk recovery properties are enhanced.

In the case where the crimped conjugate fiber contained in a fiber webis the latently crimpable conjugate fiber, the temperature is set so asto be within a range in which crimps are developed. For example, if themelting peak temperature of polybutene-1 is Tm, the temperature is setso as to be within a range of Tm−10 (° C.) to lower than the meltingpoint of the second component, preferably Tm−10 (° C.) to Tm+60 (° C.),particularly preferably Tm (° C.) to Tm+50 (° C.), and most preferably130 to 160° C. Due to the thermal processing, at least one resincomponent contained in the first component of the latently crimpableconjugate fiber melts, and pieces of the constituent fiber are thermallyfused to each other. In particular, it is preferable that when pieces ofthe constituent fiber are thermally fused to each other by allowing atleast polybutene-1 of the latently crimpable conjugate fiber to melt,more rigid intersections where pieces of the fiber meet each other canbe formed, and bulk recovery properties are enhanced.

It is preferable that the nonwoven fabric has a residual compression setrate measured according to JIS-K-6400-4 A of 45% or less, and morepreferably 35% or less. The residual compression set rate shows theextent of change of the hardness of the nonwoven fabric when heated to70° C. The smaller the value, the more the deterioration of the fiber orthe nonwoven fabric by heat is suppressed, thus indicating excellentbulk recovery properties.

It is preferable that the nonwoven fabric has a residual repetitivecompression set rate measured according to JIS-K-6400-4 B of 15% orless, and more preferably 12% or less. The residual repetitivecompression set rate shows the extent of change of the hardness of thenonwoven fabric when 50% compression is repeated 80000 times. Thesmaller the value, the more the deterioration of the fiber or thenonwoven fabric caused by compression is suppressed, thus indicatingexcellent bulk recovery properties.

The fiber product of the present invention at least partially containsthe fiber assembly, and is formed into hard stuffing, bedding, vehicleseats, chairs, shoulder pads, brassiere pads, garments, sanitarymaterials, packaging materials, wet wipes, filters, sponge-like porouswiping materials, sheet-like wiping materials, and wadding.

EXAMPLE

The present invention shall be described in more detail below by way ofexamples. However, the present invention is not limited to theseexamples.

The measurement methods and the evaluation methods used in the examplesare as follows.

Q value

I. Analyzers used

(i) Cross-fractionation apparatus “CFC T-100” (hereinafter referred toas CFC) manufactured by DIA Instruments Co., Ltd.

(ii) Fourier transform infrared absorption spectrometer (FT-IR) “1760X”manufactured by PerkinElmer, Inc.

A fixed wavelength infrared spectrophotometer attached as a detector ofthe CFC was removed and replaced by the FT-IR spectrometer, and theFT-IR spectrometer was used as a detector. The transfer line from theoutlet for a solution eluted from the CFC to the FT-IR spectrometer was1 m, and the temperature was maintained at 140° C. during measurement.The flow cell attached to the FT-IR spectrometer had an optical pathlength of 1 mm and an optical path diameter of 5 mm φ, and thetemperature was maintained at 140° C. during measurement.

(iii) Gel permeation chromatography (GPC)

Three GPC columns “AD806MS” manufactured by Showa Denko K.K. connectedin series were used in the latter portion of the CFC.

II. CFC measurement conditions

(i) Solvent: ortho-dichlorobenzene (ODCB)

(ii) Sample concentration: 1 mg/ml

(iii) Injection amount: 0.4 ml

(iv) Column temperature: 140° C.

(v) Solvent flow rate: 1 ml/min

III. FT-IR measurement conditions

After the beginning of elution of a sample solution from the GPC in thelatter portion of the CFC, FT-IR measurement was performed under thefollowing conditions, and GPC-IR data was collected.

(i) Detector: MCT

(ii) Resolution: 8 cm⁻¹

(iii) Measurement interval: 0.2 min (12 sec)

(iv) Number of scans per measurement: 15

IV. Post-processing and analysis of measurement results

The molecular weight distribution was determined using the absorbance at2945 cm⁻¹ obtained by the FT-IR spectrometer as a chromatogram. Theretention volume was converted to the molecular weight using a standardcurve prepared in advance with standard polystyrenes. The standardpolystyrenes used were “F380”, “F288”, “F128”, “F80”, “F40”, “F20”,“F10”, “F4”, “F1”, “A5000”, “A2500”, and “A1000”, all manufactured byTosoh Corporation. A calibration curve was created by injecting 0.4 mlof a solution in which 0.5 mg/ml of a standard polystyrene was dissolvedin

ODCB (containing 0.5 mg/ml of BHT). The calibration curve employed acubic equation obtained by approximation using the least-squares method.The conversion to the molecular weight employed a universal calibrationcurve in reference to Sadao Mori, “Size Exclusion Chromatography”(Kyoritsu Shuppan). The following numerical values were used in theviscosity formula ([θ]=K×Mα) used herein.

(i) In formation of calibration curve using standard polystyrenes

K=0.000138, α=0.70

(ii) In measurement of polypropylene samples

K=0.000103, α=0.78

Above, measurements were performed according to gel permeationchromatography (GPC), but measurements may be performed using anothermodel. In such a case, measurements are performed simultaneously with“MG03B” manufactured by Japan Polypropylene Corporation as described inthe 2005 Catalogue for Commercial Transaction of Plastic MoldingMaterials (Chemical Daily Co., Ltd., published on Aug. 30, 2004), thevalue when the MG03B shows 3.5 is used as a blank condition, and theconditions are adjusted to perform the measurements.

Spinnability During Melt Spinning

The spinnability of each crimped conjugate fiber was evaluated based onthe conditions of occurrence and the frequency of occurrence of a threadbreak when melt spinning was continuously performed for 30 minutes usingthe following criteria:

A: The number of thread breaks was 0 to 2 during continuous meltspinning for 30 minutes, and spinnability was good.

B: The number of thread breaks was 3 to 5 during continuous meltspinning for 30 minutes, but not detrimental to the processing.

C: The number of thread breaks was 6 or greater during continuous meltspinning for 30 minutes, or a large number of thread breaks occurred,making it impossible to carry out spinning.

Stretchability

The stretchability of a crimped conjugate fiber was evaluated based onthe conditions of occurrence of a thread break in a stretching step andthe passability through a starer-box crimper used for imparting crimpsusing the following criteria:

A: Few thread breaks occurred in a stretching step, and a thread readilypassed through a stuffer-box crimper, and thus there was absolutely noproductivity problem.

B: Thread breaks occurred in a stretching step or stuffer-box crimperclogging occurred, but not detrimental to productivity.

C: Thread breaks occurred frequently, and a thread wound around astretching bath and a stretching roll, or clogging inside a stuffer-boxcrimper or at the outlet frequently occurred, and thus severely impairedproductivity.

Staple Fiber Spreadability

The staple fiber spreadability of a crimped conjugate fiber wasevaluated based on the card processability (cardability, conditions ofnep generation, and texture of resulting web) when collecting a web bysubjecting 100 mass % of a crimped conjugate fiber to a parallel cardusing the following criteria:

A: A fiber easily passed through a parallel card, few neps wereproduced, and thus a web having good texture was obtained.

B: Some neps were generated, but the texture of a web was not affectedthat much.

C: Cardability was poor, or large amounts of neps were generated, andthus no web was obtained.

Staple fiber crimp formability of actualized crimping conjugate fiber

A tow after completion of a drying step (annealing and drying step at100° C. for 15 minutes) was visually inspected, and the staple fibercrimp formability of actualized crimping conjugate fibers was evaluatedusing the following criteria:

A: Three-dimensional crimps were developed, and it was easy to identifythe shape of spiral crimps and/or wavy crimps.

B: Three-dimensional crimps were developed, but it was fairly difficultto identify the shape of spiral crimps and/or wavy crimps, and serratedcrimps were also concomitantly present.

C: It was not possible to identify either mechanical crimps (serratedcrimps) or three-dimensional crimps (spiral crimps and/or wavy crimps),and most of the crimps had disappeared.

Staple fiber crimp formability of latently crimpable conjugate fiber

A tow after completion of a drying step (annealing and drying step at100° C. for 15 minutes) was visually inspected, and the staple fibercrimp formability of latently crimpable conjugate fibers was evaluatedusing the following criteria:

A: Mechanical crimps imparted by a stuffer-box crimper had notdisappeared, and it was easy to identify the serrated shape.

B: Mechanical crimps imparted by a stuffer-box crimper had slightlydisappeared, and there were portions where the serrated shape was notobserved.

C: It was not possible to identify either mechanical crimps (serratedcrimps) or three-dimensional crimps (spiral crimps and/or wavy crimps),and most of the crimps had disappeared.

Crimp formability after thermal processing of actualized crimpingconjugate fiber

Each crimped conjugate fiber (100 mass %) was subjected to a parallelcard to collect a web, and the web was treated at a processingtemperature of 150° C. for 30 seconds with a convection heating machineand then visually inspected in order to evaluate the crimp formabilityafter thermal processing of an actualized crimping conjugate fiber usingthe following criteria:

A: Developed three-dimensional crimps had not disappeared, and it waseasy to identify the shape of spirals crimp and/or wavy crimps.

B: Developed three-dimensional crimps had partially disappeared, but itwas possible to identify the shape of spiral crimps and/or wavy crimps.

C: Developed three-dimensional crimps had mostly disappeared, and it wasdifficult to identify the shape of crimps.

Crimp formability after thermal processing of latently crimpableconjugate fiber

A crimped conjugate fiber (100 mass %) was subjected to a parallel cardto collect a web, and the web was treated at a processing temperature of150° C. for 30 seconds with a convection heating machine and thenvisually inspected in order to evaluate the crimp formability afterthermal processing of a latently crimpable conjugate fiber using thefollowing criteria:

A: Three-dimensional crimps were developed due to thermal treatment, andit was easy to identify the shape of spiral crimps and/or wavy crimps.

B: Three-dimensional crimps were poorly developed, or three-dimensionalcrimps developed due to heat were partially disappeared, but it waspossible to identify the shape of spiral crimps and/or wavy crimps.

C: Three-dimensional crimps were poorly developed, or three-dimensionalcrimps were developed due to heat were mostly disappeared, and it wasdifficult to identify the shape of crimps.

Measurement of melting points (Tf1, Tf2) of each component afterspinning

Using a DSC manufactured by Seiko Instruments Inc., a sample in anamount of 3.2 mg was heated at a heating rate of 10° C./min fromordinary temperature to 200° C. (provided that the temperature wasincreased to 300° C. in the case where a polyester-based polymer wasused as the second component), and then cooled at a cooling rate of 10°C./min to 40° C. From the resulting heat of fusion curve, the meltingpoint Tf1 of the first component after spinning and the melting pointTf2 of the second component after spinning were obtained. Regarding themelting point after spinning, in the case where two peaks appeared, thepeak on the lower temperature side was regarded as the melting point(Tf1) of the first component, and the peak on the higher temperatureside was regarded as the melting point (Tf2) of the second component. Inthe case where three or more peaks appeared when measuring the meltingpoint after spinning, the last peak, i.e., the peak on the highertemperature side, was regarded as the melting point (Tf2) of the secondcomponent, and the other peaks were regarded as the melting points (Tf1)after spinning of the respective polymers constituting the firstcomponent.

Residual Compression Set Rate

The set rate after compression at a temperature of 70° C.±1° C. at acompression rate of 50% for 22 hours was measured according toJIS-K-6400-4 A and was regarded as a residual compression set rate. Allthe thickness measurement was carried out while no load was applied tothe test pieces in the thickness direction, and a metal bench rule asspecified in JIS-B-7516 was used for measurement.

Residual Repetitive Compression Set Rate

The set rate after compression 80000 times at a temperature of 23° C. ata compression rate of 50% was measured according to JIS-K-6400-4 B andwas regarded as a residual repetitive compression set rate. All thethickness measurement was carried out while no load was applied to thetest pieces in the thickness direction, and a metal bench rule asspecified in JIS-B-7516 was used for measurement.

Polymers used in the examples are as follows:

(1) PET (“T200E” manufactured by Toray Industries, Inc., melting peaktemperature (melting point): 255° C., IV value: 0.64)

(2) PP-A (“SA03E” manufactured by Japan Polypropylene Corporation,melting peak temperature (melting point): 160° C., MFR230: 20 g/10 min,Q value: 5.6)

(3) PP-B (“SAOlA” manufactured by Japan Polypropylene Corporation,melting peak temperature (melting point): 160° C., MFR230: 9 g/10 min, Qvalue: 3.2)

(4) PB-1 (“DPO401M” manufactured by SunAllomer Ltd., melting peaktemperature (melting point): 123° C., MFR190: 20 g/10 min)

(5) LLDPE-A (“Kernel” (registered trademark) “KS560T” manufactured byJapan Polyethylene Corporation [linear low density polyethylenesynthesized by a high-pressure method using a metallocene catalyst],melting peak temperature (melting point): 90° C., MFR190: 16.5 g/10 min,density: 0.898 g/cm³, Q value: 2.5, flexural modulus: 62 MPa)

(6) LLDPE-B (“420SD” manufactured by Ube Maruzen Polyethylene Co., Ltd.[linear low density polyethylene synthesized by a gas phase method usinga metallocene catalyst], melting peak temperature (melting point): 118°C., MFR190° C.: 7 g/10 min, density: 0.918 g/cm³, Q value: 3.0, flexuralmodulus: 280 MPa)

(7) LLDPE-C (“Kernel” (registered trademark) “KC571” manufactured byJapan Polyethylene Corporation [linear low density polyethylenesynthesized by a high-pressure method using a metallocene catalyst],melting peak temperature (melting point): 100° C., MFR190: 12 g/10 min,density: 0.907 g/cm³, Q value: 2.2, flexural modulus: 110 MPa)

(8) LLDPE-D (“Harmorex” (registered trademark) “NJ744N” manufactured byJapan Polyethylene Corporation [linear low density polyethylenesynthesized by a gas phase method using a metallocene catalyst], meltingpeak temperature (melting point): 120° C., MFR190: 12 g/10 min, density:0.911 g/cm³, Q value: 2.5, flexural modulus: 120 MPa)

(9) LLDPE-E (“631J” manufactured by Ube Maruzen Polyethylene Co., Ltd.[linear low density polyethylene synthesized by a gas phase method usinga metallocene catalyst], melting peak temperature (melting point): 121°C., MFR190: 20 g/10 min, density: 0.931 g/cm³, Q value: 2.9, flexuralmodulus: 600 MPa) (10) LDPE (“LJ802” manufactured by Japan PolyethyleneCorporation, melting peak temperature (melting point): 106° C., MFR190:22 g/10 min, density: 0.918 g/cm³)

(11) PPR-1 (polypropylene-based thermoplastic elastomer, “Notio”(registered trademark) “2070” manufactured by Mitsui Chemicals, Inc.,[olefin-based thermoplastic elastomer synthesized using a metallocenecatalyst], melting peak temperature (melting point): 138° C., Shore Ahardness (ASTM D 2240): 75, MFR230: 6 g/10 min, density: 0.867 g/cm³)

(12) PPR-2 (polyolefin-based thermoplastic elastomer, “Adflex V109F”manufactured by Basell, melting peak temperature (melting point): 143°C., Shore D hardness (ASTM D 2240): 41, MFR230: 12 g/10 min, density:0.880 g/cm³) (13) BP (butene-propylene copolymer, “5C37F” manufacturedby SunAllomer Ltd., melting peak temperature (melting point): 132° C.,MFR230: 6 g/10 min) (14) EMAA (“Nucrel” (registered trademark)manufactured by Du Pont-Mitsui, density: 0.940 g/cm³, melting peaktemperature (melting point): 88° C., MFR190: 10 g/10 min)

Above, the IV value refers to the above-described limiting viscosity,and MFR230 refers to a melt flow rate measured at 230° C. under 21.18N(2.16kgf) in accordance with JIS-K-7210. MFR190 refers to a melt flowrate measured at 190° C. under 21.18N (2.16kgf) in accordance withJIS-K-7210.

A description of the manufacturing conditions of crimped conjugatefibers is as follows.

(A) Extrusion temperature: 300° C. for the second component polymer,250° C. for the first component polymer, nozzle spinneret temperature:270° C.

(B) Withdrawing rate: 500 m/min

(C) Number of nozzle holes: 600

(D) Combination ratio: core/sheath =55/45 (volume ratio)

(E) Unstretched fiber fineness: 10 dtex

(F) Stretching temperature: wet 80° C.

(G) Stretch ratio: 2.3

(H) Crimps: 12 to 16 per 25 mm

(I) Annealing temperature (drying temperature), time: 100° C., 15 min

(J) Product fineness (single fiber): 6.0 dtex

(K) Fiber length: 51 mm

Production Conditions of Nonwoven Fabric

A crimped conjugate fiber (100 mass %) was subjected to a parallel cardto collect a web, and the web was treated at a processing temperature of150° C. for 30 seconds with a convection heating machine, thus giving anonwoven fabric having a unit weight of 500 g/m².

Example 1

A crimped conjugate fiber was prepared under the above-described crimpedconjugate fiber production conditions using only PP-A as the secondcomponent and a mixture of PB-1 and LLDPE-A having a mass ratio ofPB-1/LLDPE-A=92/8 as the first component. Next, a nonwoven fabric wasprepared under the above-described nonwoven fabric production conditionsusing the resulting crimped conjugate fiber.

Example 2

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and LLDPE-A having a mass ratio ofPB-1/LLDPE-A=97/3 was used as the first component.

Example 3

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and LLDPE-A having a mass ratio ofPB-1/LLDPE-A=95/5 was used as the first component.

Example 4

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the secondcomponent.

Example 5

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and LLDPE-A having a mass ratio ofPB-1/LLDPE-A=80/20 was used as the first component.

Example 6

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and LLDPE-B having a mass ratio ofPB-1/LLDPE-B=92/8 was used as the first component.

Example 7

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and LLDPE-C having a mass ratio ofPB-1/LLDPE-C=92/8 was used as the first component.

Example 8

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=95/5 was used as the second component.

Example 9

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=75/25 was used as the secondcomponent.

Example 10

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-B and PPR-1having a mass ratio of PP-B/PPR-1=85/15 was used as the secondcomponent.

Example 11

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-2having a mass ratio of PP-A/PPR-2=85/15 was used as the secondcomponent.

Example 12

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PB-1 and LLDPE-Dhaving a mass ratio of PB-1/LLDPE-D=92/8 was used as the firstcomponent.

Example 13

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PB-1 and LLDPE-Ehaving a mass ratio of PB-1/LLDPE-E=92/8 was used as the firstcomponent.

Example 14

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PB-1, LLDPE-D, andEMAA having a mass ratio of PB-1/LLDPE-D/EMAA=90/5/5 was used as thefirst component.

Example 15

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that only PET was used as the secondcomponent and a mixture of PB-1 and LLDPE-D having a mass ratio ofPB-1/LLDPE-D=92/8 was used as the first component.

Example 16

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that only PET was used as the secondcomponent.

Example 17

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that only PET was used as the secondcomponent and a mixture of PB-1, LLDPE-D, and EMAA having a mass ratioof PB-1/LLDPE-D/EMAA=90/5/5 was used as the first component.

Example 18

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that only PET was used as the secondcomponent and a mixture of PB-1, LLDPE-A, and EMAA having a mass ratioof PB-1/LLDPE-A/EMAA=90/5/5 was used as the first component.

Comparative Example 1

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand only PB-1 was used as the first component.

Comparative Example 2

An attempt was made to prepare a crimped conjugate fiber in the samemanner as in Example 1 except that a mixture of PP-A and PPR-1 having amass ratio of PP-A/PPR-1=85/15 was used as the second component and amixture of PB-1 and LLDPE-A having a mass ratio of PB-1/LLDPE-A=70/30was used as the first component, but spinnability was poor, and threadbreaks frequently occurred immediately below the spinning nozzle, and itwas thus not possible to prepare a spun filament.

Comparative Example 3

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=99/1 was used as the second componentand a mixture of PB-1 and LDPE having a mass ratio of PB-1/LDPE =90/10was used as the first component.

Comparative Example 4

An attempt was made to prepare a crimped conjugate fiber and a nonwovenfabric in the same manner as in Example 1 except that a mixture of PP-Aand PPR-1 having a mass ratio of PP-A/PPR-1=85/15 was used as the secondcomponent and a mixture of PB-1 and EMAA having a mass ratio ofPB-1/EMAA=94/6 was used as the first component, but the stretchabilityof the spun filament was poor. In addition, crimp formability afterperforming thermal processing in order to form a nonwoven fabric waspoor, and it was thus not possible to prepare thermally adhered nonwovenfabric having good cushioning properties.

Comparative Example 5

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that a mixture of PP-A and PPR-1having a mass ratio of PP-A/PPR-1=85/15 was used as the second componentand a mixture of PB-1 and BP having a mass ratio of PB-1/BP=85/15 wasused as the first component.

Comparative Example 6

An attempt was made to prepare a crimped conjugate fiber and a nonwovenfabric in the same manner as in Example 1 except that only PET was usedas the second component and a mixture of PB-1, PP-A, and EMAA having amass ratio of PB-1/PP-A/EMAA=85/10/5 was used as the first component.Although a conjugate fiber having high spinnability, stretchability, andcrimp formability was obtained, pieces of the constituent fiber did notthermally bond sufficiently to each other in thermal bonding processingat 150° C., and thus it was not possible to obtain a thermally bondednonwoven fabric.

Comparative Example 7

A crimped conjugate fiber and a nonwoven fabric were prepared in thesame manner as in Example 1 except that only PET was used as the secondcomponent and a mixture of PB-1 and EMAA having a mass ratio ofPB-1/EMAA=92/8 was used as the first component.

Tables 1 to 4 below show the results of the eccentricity, spinnabilityduring melt spinning, staple fiber spreadability, staple fiber crimpformability, and crimp formability after thermal processing of theresulting crimped conjugate fibers as well as the initial thickness,unit weight, residual repetitive compression set, and residualcompression set of the nonwoven fabrics of Examples 1 to 18 andComparative Examples 1 to 7. The crimped conjugate fibers of Examples 1to 4, 6 to 9, and 11 to 18 were actualized crimping conjugate fibers,have wavy crimps as shown in FIG. 2A or spiral crimps, or have both wavycrimps and spiral crimps, and the number of crimps was 12 to 18 per 25mm. The crimped conjugate fibers of Examples 5 and 10 were latentlycrimpable conjugate fibers in which three-dimensional crimps have beendeveloped due to thermal processing performed when preparing a nonwovenfabric, have at least one of the wavy crimps as shown in FIG. 2A and thespiral crimps.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Second Resin 1 PP-A PP-APP-A PP-A PP-A PP-A component Resin 2 — PPR-1 PPR-1 PPR-1 PPR-1 PPR-1(Core resin) Resin 1:Resin 2 100:0 85:15 85:15 85:15 85:15 85:15 Meltingpoint (Tf2) 163.5 — — — — 162.9 after spinning (° C.) First Resin 1 PB-1PB-1 PB-1 PB-1 PB-1 PB-1 component Resin 2 LLDPE-A LLDPE-A LLDPE-ALLDPE-A LLDPE-A LLDPE-B (Sheath Resin 3 — — — — — — resin) Resin 1:Resin2:Resin 3  92:8 97:3  95:5  92:8  80:20 92:8  Melting point (Tf1) 123.2— — — — 121.7 after spinning (° C.) Eccentricity (%) 25 25 25 25 25 25Spun thread A-C A A A A B A break Stretchability A-C A A A A A A Staplefiber A-C A A A A B A spreadability Staple fiber A-C A A A A A A crimpformability Crimp (A-C) A A A A A A formation Actual or latent ActualActual Actual Actual Latent Actual after thermal crimps crimps crimpscrimps crimps crimps processing Initial (mm) 25 25 25 25 25 25 thicknessUnit weight (g/m²) 500 500 500 500 500 500 Residual (%) 11.7 10.3 11.29.7 11.8 11.9 repetitive compression set Residual (%) 33.4 26.1 29.230.0 33.5 33.7 compression set

TABLE 2 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Second Resin 1 PP-A PP-APP-A PP-B PP-A PP-A component Resin 2 PPR-1 PPR-1 PPR-1 PPR-1 PPR-2 —(Core resin) Resin 1:Resin 2 85:15 95:5 75:25 85:15 85:15 100:0 Meltingpoint (Tf2) 162.6 — — — — 162.0 after spinning (° C.) First Resin 1 PB-1PB-1 PB-1 PB-1 PB-1 PB-1 component Resin 2 LLDPE-C LLDPE-A LLDPE-ALLDPE-A LLDPE-A LLDPE-D (Sheath Resin 3 — — — — — — resin) Resin 1:Resin2:Resin 3 92:8  92:8 92:8  92:8  92:8   92:8 Melting point (Tf1) 123.5 —— — — 121.9 after spinning (° C.) Eccentricity (%) 25 25 25 25 25 25Spun thread A-C A A A A A A break Stretchability A-C A A A A A A Staplefiber A-C A A A A B A spreadability Staple fiber A-C A A A A A A crimpformability Crimp (A-C) A A A A A A formation Actual or latent ActualActual Actual Latent Actual Actual after thermal crimps crimps crimpscrimps crimps crimps processing Initial (mm) 25 25 25 25 25 25 thicknessUnit weight (g/m²) 500 500 500 500 500 500 Residual (%) 9.5 10.5 10.711.4 11.2 11.0 repetitive compression set Residual (%) 28.5 30.0 31.331.8 29.2 31.4 compression set

TABLE 3 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Second Resin 1 PP-APP-A PET PET PET PET component Resin 2 — — — — — — (Core resin) Resin1:Resin 2 100:0 100:0 100:0 100:0 100:0 100:0 Melting point (Tf2) 163.0— — — — — after spinning (° C.) First Resin 1 PB-1 PB-1 PB-1 PB-1 PB-1PB-1 component Resin 2 LLDPE-E LLDPE-D LLDPE-D LLDPE-A LLDPE-D LLDPE-A(Sheath Resin 3 — EMAA — — EMAA EMAA resin) Resin 1:Resin 2:Resin 3 92:8 90:5:5  92:8 92:8 90:5:5 90:5:5 Melting point (Tf1) 120.8 — — — —— after spinning (° C.) Eccentricity (%) 25 25 25 25 25 25 Spun threadA-C A A A A A A break Stretchability A-C A A A A A A Staple fiber A-C AA A A A A spreadability Staple fiber A-C A A A A A A crimp formabilityCrimp (A-C) A A A A A A formation Actual or latent Actual Actual ActualActual Actual Actual after thermal crimps crimps crimps crimps crimpscrimps processing Initial (mm) 25 25 25 25 25 25 thickness Unit weight(g/m²) 500 500 500 500 500 500 Residual (%) 12.2 10.8 10.1 10.4 9.8 9.7repetitive compression set Residual (%) 35.0 31.2 39.8 39.8 39.5 39.8compression set

TABLE 4 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex.4 Ex. 5 Ex. 6 Ex. 7 Second Resin 1 PP-A PP-A PP-A PP-A PP-A PET PETcomponent Resin 2 PPR-1 PPR-1 PPR-1 PPR-1 PPR-1 — — (Core resin) Resin1:Resin 2 85:15 85:15 99:1  85:15 85:15 100:0 100:0 Melting point (Tf2)— — — — — 250.4 — after spinning (° C.) First Resin 1 PB-1 PB-1 PB-1PB-1 PB-1 PB-1 PB-1 component Resin 2 — LLDPE-A LDPE EMAA BP PP-A EMAA(Sheath Resin 3 — — — — — EMAA — resin) Resin 1:Resin 2:Resin 3 100:0 70:30 90:10 94:6  85:15 85:10:5  92:8 Melting point (Tf1) — — — — —162.7 — after spinning (° C.) 119.0 Eccentricity (%) 25 25 25 25 25 2525 Spun thread A-C A C A B B A B break Stretchability A-C B — A B B A CStaple fiber A-C A — B A B A A spreadability Staple fiber A-C A — A A BA A crimp formability Crimp (A-C) A — A C A A A formation Actual orlatent Latent Latent Latent Actual Actual after thermal crimps crimpscrimps crimps crimps processing Initial (mm) 25 — 25 — — — 25 thicknessUnit weight (g/m²) 500 — 500 — — — 500 Residual (%) 11.6 — 12.4 — — —9.7 repetitive compression set Residual (%) 33.8 — 34.7 — — — 39.8compression set

A comparison of Examples 1 to 18 of Tables 1 to 3 with ComparativeExamples 1 to 7 of Table 4 confirms that, with crimped conjugate fibersin which the first component contained PB-1, addition of linear lowdensity polyethylene to PB-1 brought about the effect of enhancing thestretchability, the staple fiber spreadability, the staple fiber crimpformability, and like properties of PB-1. This can be confirmed from thefact that conjugate fibers in which the first component was composedsolely of PB-1 and conjugate fibers in which polymers other than linearlow density polyethylene were added to PB-1 as shown in ComparativeExamples 1, 4, 5, and 7 of Table 4 had poor stretchability (Bevaluation), whereas stretchability was good (A evaluation) in allExamples. The conjugate fiber to which low density polyethylene (LDPE)was added to the first component did not have good staple fiberspreadability, thus confirming that addition of linear low densitypolyethylene as a polymer to be added to the first component containingpolybutene-1 as the main ingredient enables crimped conjugate fibershaving not only good spinnability and stretchability but also goodstaple fiber crimp formability, and crimp formability after thermalprocessing, i.e., all such properties were good, to be obtained.

It can be confirmed from Examples 1 to 18 that, with the crimpedconjugate fiber of the present invention, when the first component was aresin component containing polybutene-1 and linear low densitypolyethylene, a nonwoven fabric that used the resulting conjugate fiberhad little residual repetitive compression set irrespective of whetherthe second component was either a polyolefin-based polymer or apolyester-based polymer. Therefore, in the crimped conjugate fiber ofthe present invention, the second component that constitutes the innerportion of the conjugate fiber is not particularly limited, and itappears that the second component, while not being limited to apolyester-based polymer or a polyolefin-based polymer, is usable insofaras it is a polymer having a melting peak temperature at least 20° C.higher than the melting peak temperature of polybutene-1 or a polymerhaving a melting initiation temperature of 120° C. or higher and havingexcellent bending strength and bending plasticity.

Regarding crimped conjugate fibers in which the first componentcontained PB-1, for adding linear low density polyethylene to the firstcomponent, conjugate fibers in which linear low density polyethylene wasadded in a proportion of 20 mass % relative to the first component hadgood spinnability, whereas conjugate fibers to which linear low densitypolyethylene was added in a proportion of 30 mass % to the firstcomponent had very poor spinnability. Therefore, it can be presumed froma comparison of Example 5 and Comparative Example 2 that there is anupper limit to the amount of linear low density polyethylene added, andthe upper limit to the amount is less than 30 mass %, and preferably 25mass % or less.

It can be confirmed that, with the crimped conjugate fibers of Examples1 to 18, the crimp formability of the resulting crimped conjugate fibersand the resistance to residual repetitive compression set and theresistance to residual compression set of nonwoven fabrics that used thecrimped conjugate fibers were enhanced. In particular, it can beconfirmed that the crimped conjugate fibers of Examples 2 to 4, 7 to 9,11, 12 and 14 and nonwoven fabrics that used the crimped conjugatefibers had a rate of residual repetitive compression set of 11.5% orless and a rate of residual compression set of 31.5% or less, which weresignificantly more improved than those of the nonwoven fabric ofComparative Example 1. A comparison of Examples 2 to 4, 7 to 9, 11, 12,and 14 with Examples 6 and 13 shows that the residual repetitivecompression set and the residual compression set of nonwoven fabricsthat used the crimped conjugate fibers of Examples 6 and 13 in whichlinear low density polyethylenes having a relatively high density and ahigh flexural modulus were used were increased, and therefore it ispresumed that it is preferable for the crimped conjugate fiber of thepresent invention that linear low density polyethylene to be added tothe first component is linear low density polyethylene having a lowerdensity and a lower flexural modulus insofar as thermal bondingproperties and heat resistance are not affected.

As shown in Comparative Example 6, it can be confirmed that regarding acrimped conjugate fiber in which the first component containing PB-1,the spinnability and the stretchability of PB-1 were enhanced also in aconjugate fiber in which polypropylene was added to the first component,and a crimped conjugate fiber having excellent staple fiberspreadability, staple fiber crimp formability, and staple fiber crimpformability after thermal processing was obtained. However, sincepolypropylene, which had a higher melting point than PB-1, was added tothe first component in the crimped conjugate fiber of ComparativeExample 6, the apparent melting point of the first component wasincreased. As a result, it was confirmed that pieces of the conjugatefiber were not sufficiently bond to each other under this thermalbonding processing condition. Therefore, a comparison of the meltingpoints (Tf1) of the first components after spinning of Examples 1 to 18and Comparative Example 6, in particular Examples 1, 6, 7, 12, and 13and Comparative Example 6 confirms that, in the case of performingthermal bonding processing at lower temperatures or thermal processingto attain higher bonding strength in a shorter period of time, it ismost suitable to add linear low density polyethylene to the firstcomponent in a crimped conjugate fiber in which the first componentcontains PB-1.

INDUSTRIAL APPLICABILITY

A fiber assembly that uses the crimped conjugate fiber of the presentinvention has both excellent initial bulk and bulk recovery propertiesand is preferably used in applications such as cushioning materials andlike hard stuffing, sanitary materials, packaging materials, materialsfor cosmetic products, low-density non-woven fabric products such aswomen's brassiere pads and shoulder pads, wiping materials for peopleand non-human objects for which urethane foam and urethane sponge havegenerally been used, powdery or liquid cosmetic coating materials, heatinsulating materials, and sound absorbing materials. Moreover, thecrimped conjugate fiber of the present invention has excellentelasticity and shape recoverability, and is therefore preferably used aswadding for various kinds of bedding such as blankets and mattresses andclothing articles. In the crimped conjugate fiber of the presentinvention in which a polyolefin-based polymer is used as the secondcomponent, which is one embodiment of the crimped conjugate fiber of thepresent invention, all the resin components constituting the conjugatefiber are composed of polyolefin-based polymers, and therefore afterbeing used as the hard stuffing, wadding, and low-density nonwovenfabric products, it is easy to collect the crimped conjugate fiber as acomponent composed of polyolefin-based polymers, reuse it as a resinmaterial, or reuse it as a polyolefin-based fiber, and preferably isused as various fiber assembly products for which separate collectionafter use and reuse of components are desired.

LIST OF REFERENCE NUMERALS

-   1 First component-   2 Second component-   3 Centroid position of second component-   4 Centroid position of conjugate fiber-   5 Radius of conjugate fiber-   10 Conjugate fiber

1. A crimped conjugate fiber comprising a first component and a secondcomponent, the first component comprising polybutene-1 and linear lowdensity polyethylene, the content of the linear low density polyethylenein the first component is 2 to 25 mass %, the second componentcomprising a polymer having a melting peak temperature at least 20° C.higher than a melting peak temperature of polybutene-1 or a polymerhaving a melting initiation temperature of 120° C. or higher, whenviewed from a fiber cross-section, the first component occupies at least20% of a surface of the conjugate fiber, and a centroid position of thesecond component not overlapping a centroid position of the conjugatefiber, and the conjugate fiber is an actualized crimping conjugate fiberin which three-dimensional crimps have been developed or a latentlycrimpable conjugate fiber in which three-dimensional crimps aredeveloped by heating.
 2. The crimped conjugate fiber according to claim1, wherein the three-dimensional crimps are at least one selected fromwavy crimps and spiral crimps.
 3. The crimped conjugate fiber accordingto claim 1, wherein the linear low density polyethylene is a copolymerpolymerized with α-olefin using a metallocene catalyst.
 4. The crimpedconjugate fiber according to claim 1, wherein the linear low densitypolyethylene has a melting peak temperature obtained from DSC measuredaccording to JIS-K-7121 of 80 to 130° C. and a density measuredaccording to JIS-K-7112 of 0.88 to 0.92 g/cm³.
 5. The crimped conjugatefiber according to claim 1, wherein the linear low density polyethylenehas a flexural modulus measured according to JIS-K-7171 of 20 to 300MPa.
 6. The crimped conjugate fiber according to claim 1, wherein thepolymer having a melting peak temperature at least 20° C. higher than amelting peak temperature of polybutene-1 or the polymer having a meltinginitiation temperature of 120° C. or higher contained in the secondcomponent is a polyolefin-based polymer.
 7. The crimped conjugate fiberaccording to claim 6, wherein the polyolefin-based polymer contained inthe second component is homopolypropylene, and the homopolypropylene iscontained in the second component in a proportion of 75 to 100 mass %,when the entire second component being 100 mass %.
 8. The crimpedconjugate fiber according to claim 1, wherein the polymer having amelting peak temperature at least 20° C. higher than a melting peaktemperature of polybutene-1 or the polymer having a melting initiationtemperature of 120° C. or higher contained in the second component is apolyester-based polymer.
 9. A fiber assembly comprising a crimpedconjugate fiber in a proportion of 30 mass % or greater, the crimpedconjugate fiber comprising a first component and a second component, thefirst component comprising polybutene-1 and linear low densitypolyethylene, the content of the linear low density polyethylene in thefirst component is 2 to 25 mass %, the second component comprising apolymer having a melting peak temperature at least 20° C. higher than amelting peak temperature of polybutene-1 or a polymer having a meltinginitiation temperature of 120° C. or higher, when viewed from a fibercross-section, the first component occupies at least 20% of a surface ofthe conjugate fiber, and a centroid position of the second component notoverlapping a centroid position of the conjugate fiber, and theconjugate fiber is an actualized crimping conjugate fiber in whichthree-dimensional crimps have been developed or a latently crimpableconjugate fiber in which three-dimensional crimps are developed byheating.
 10. The fiber assembly according to claim 9, comprising, inaddition to the crimped conjugate fiber, at least one fiber selectedfrom synthetic fibers, chemical fibers, natural fibers, and inorganicfibers.
 11. A fiber product at least partially contains the fiberassembly of claim 9 and formed into hard stuffing, bedding, a vehicleseat, a chair, a shoulder pad, a brassiere pad, a cloth, a hygienicmaterial, a packaging material, a wet wipe, a filter, a sponge-likeporous wiping material, a sheet-like wiping material, or wadding.